US2885302A

US2885302A - Method of making transfer sheets and resulting article

Info

Publication number: US2885302A
Application number: US779892A
Authority: US
Inventors: Phillpotts George Cordery
Original assignee: Caribonum Ltd
Current assignee: Caribonum Ltd
Priority date: 1956-08-14
Filing date: 1958-12-12
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05
Also published as: GB855867A

Description

METHOD OF MAKING TRANSFER SHEETS AND RESULTING ARTICLE Filed Deo. 12', 1958 United States Patent O "ice METHOD F MAKING TRANSFER SHEETS AND RESULTING ARTICLE George Cordery Phillpotts, Kingston Hill, Surrey, England, assignor to Caribonum Limited, Leyton, London, England, a British company Application December 12, 1958, Serial No. 779,892

Claims priority, application Great Britain August 14, 1956 Claims. (Cl. 117-36) This application is a continuation-in-part of my application Serial No. 673,013, tiled July 19, 1957.

The present invention relates to manifolding and is concerned with improvements in manifolding paper, and transfer sheet material in general, which is of the substantially colourless type.

Manifolding papers are known wherein each sheet of paper has upon its underside an active coating containing a colourless, colour-developing substance. For copying purposes, this is placed upon another sheet of paper on the upper side of which is a reactive receptive coating, the active and reactive receptive coatings being such that substantially colourless material is transferred from the active coating and thereupon develops a contrasting mark on the reactive receptive coating. A reasonable multiplicity of copies, say six, may be obtained by using a pack of such sheets and this is also the case where the rst sheet is coated upon the underside only and for convenience is known as an A sheet, the next live sheets are coated upon the upper face with a reactive receptive coating and upon the under face with an active coating and are known as B sheets, and the nal sheet is coated, upon its upper face only, with a reactive receptive coating and is known as a C sheet.

It has been proposed to coat the active sheet with small globules consisting of an outer skin of, for example, gelatin which has been suitably hardened with formaldehyde and, within this hardened outer skin, a small quantity of an oily material containing a colourdeveloping substance, as for example methyl violet lactone and/or benzoyl-leuco-methylene blue. These globules are mixed with a small quantity of a binding substance in water and coated on paper. When the paper so coated is brought face to face with a sheet of paper having an acid clay coated thereon, such for example as attapnlgite, and is written upon, the methyl violet lactone produces an immediate blue mark which subsequently fades, while the benzoyl-leuco-rnethylene blue slowly develops a greenish-blue colour, by what is believed to be some form of oxidation reaction. Thus, a copy is made which, starting blue, nally becomes green or bluish-green. The process of making the globules referred to above is somewhat costly; this process is referred to in United States specifications Nos. 2,712,507 and 2,730,457 and also in British specification No. 751,600.

In co-pending application No. 647,684, filed March 21, 1957, in the names of the applicant herein and D. J. Neale, it has been proposed to emulsify a solution of one or more substituted rnonoor di-leucauramines in oil substances, disperse this solution in suitable binding material, as for example gelatin or ammonium alginate, and coat this dispersion on paper with or without the addition to the emulsion of substances such as titanium White and/ or zinc oxide, but with a small quantity of an alkaline substance such as sodium carbonate. A suitable reactive receptive coating may be prepared, for example, from dextrin, blanc fixe, phosphotungstic acid ,Y 2,885,302 Patented May 5, 1959 and/or tannic acid dissolved in dibfutyl tartrate, all of which in suitable proportions are dissolved or suspended in water, coated on paper and dried, a suitable coated weight after drying being 7.5 grams per square metre. When such an active sheet is brought into contact with the reactive receptive coating on another sheet, and written upon, an immediate dense blue writing is produced which does not fade. It is foimd however, that it is difficult to prevent such sheets from marking spontaneously if such sheets are prepared in packs in the form of A, B and C sheets, unlessa subsequent process is used such for example as spraying the surface of the active sheet with a solution of for example dexnin or gum arabic in water in such a way as to leave minute globules upon the surface so that they prevent the two surfaces from coming into contact unless pressure, such as might be caused by writing instruments such as pencil, pen or typewriter, is brought to bear.

Accordingly, it is an object of the present invention to provide transfer sheet material, and a method for making it, which is not subject to this disadvantage. A further object of the invention is to provide a manifolding pack of two or more sheets of transfer material, which can be used to produce copies upon each sheet in the pack by the action of Writing upon the uppermost sheet thereof.

According to the invention, transfer sheet material for use in manifolding comprises a base web and a substantially colourless coating carried upon a surface of the base web, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete particles of pressure-responsive sponge-like material having a particle size from about 3 to about 10 microns, and the sponge-like particles having absorbed therein a colourforming fluid material containing a colourless derivative of a `dyestuf adapted to be converted into the corresponding coloured dyestuft on reaction with an acid substance, the continuous phase of the coating consisting of a dry and hard but pervious lm suciently friable to permit the colour-forming fluid material to pass therethrough, the pressure responsive, sponge-like particles being adapted normally to retain the colour-forming iluid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to writing pressure, and thereby to be transferred to a copy sheet in contact with the coated surface of the transfer sheet material.

The invention also consists in a manifolding pack which comprises at least two portions of transfer sheet material, each portion comprising a sheet of paper, at least all sheets except the lowermost sheet in the manifolding pack carrying on the lower surface thereof a substantially colourless coating, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete spray-dried particles of a pressure-responsive sponge-like material selected from the group consisting of alginates, casein and gelatin and having a particle size from about 3 to about 10 microns, and the spongelike particles having absorbed therein an oily, colour-forming iluid material containing a colourless dyestutf derivative selected from the group consisting of leucauramines and substituted leucauramines, the continuous phase of the coating consisting of a dry and hard but pervious film sufficiently friable to permit the colour-forming fluid material to pass therethrough, and at least all sheets except the uppermost sheet in the manifolding pack carrying on the upper surface thereof a coating including an acid substance, the colourless dyestulf derivative contained in the colourforming fluid material being adapted to be converted into the corresponding coloured dyestuif on reaction with the acid substance present in' the coating on the upper surface of the next underlying sheet of paper in the manifolding pack, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit the fluid material to be expressed through the friable film when the manifolding pack is subjected to writing pressure and thereby to be transferred to the aforesaid next underlying sheet of paper and to react there with the acid substance to form the coloured dyestuff in the form of visible written characters.

A further aspect of the invention comprises a method of making transfer sheet material, which comprises the steps of providing a base web, forming a substantially colourless emulsion comprising a colourless dyestuff derivative and a material adapted to form pressure-responsive, discrete sponge-like particles on spray-drying the emulsion, spray-drying the emulsion in the presence of a hardening agent to form a plurality of discrete particles of pressure-responsive sponge-like material having a particle size from about 3 to about l0 microns, the particles having absorbed therein a colour-forming fluid material containing the colourless dyestuff derivative, which is adapted to be converted into the corresponding coloured dyestuf on reaction with an acid substance, dispersing the particles in a binder therefor to form a dispersion having the binder as its continuous phase and the particles as its discontinuous phase and coating the dispersion on to one surface of the base web thereby to form a coating in which the hinder forms a dry and hard but pervious film Sulliciently friable to permit the colour-forming fluid material to pass therethrough and the pressure-responsive spongelike particles are adapted normally to retain the colourforming fluid material but to permit it to be expressed through the friable film when the transfer sheet material is subjected to writing pressure and transferred to a copy sheet in contact with the coated surface of the transfer sheet material.

It has been found that if the active emulsions, that is to say the emulsion containing leucauramines or substituted leucauramines, which may consist of these colourdeveloping substances dissolved in oils or oily substances and emulsiiied in a solution of ammonium alginate or casein or gelatin, are spray-dried in such a manner that they produce dried particles of approximately 3-6 microns in diameter, then the particles so produced do not consist of an outer shell of gelatin or casein or alginate but are of the character of minute Sponges, retaining within the pores of the sponge the solution of the colour-developing substances.

If suitable means are taken to harden the continuous phase of the emulsion, namely the casein, gelatin or ammonium or other alginate, it is found that the dried continuous phase of these particles is in itself insoluble in water and the particles may then be readily dispersed in a binding agent as for example a solution of starch in water or casein in water or gelatin in water or triethanolamine al-ginate in water and coated upon the paper. The binding agent or binder must have the properties required to form a continuous phase of a coating, when the dispersion of the particles and binder is coated upon the paper, in which coating the particles constitutes the continuous phase. If the proportion of dissolved binder is sutiiciently high but not too high, the sponge-like particles are bound in place and it is found that there is no tendency whatever to mark the reactive sheet when the active and reactive sheets are placed in contiguity unless and until the fairly concentrated pressure of a writing instrument such for example as a pen, pencil or typewriter is brought into use.

In hardening the base material of these particles, the normally well-known materials are not in all cases satisfactory; thus for example it is unsatisfactory to add formaldeyde to the Igelatin or casein solutions, since hardening takes place before the material can be spraydried. If, however, the emulsions are pumped to the spray-drier by means of proportioning pumps so thatl the formaldehyde is added to the casein or gelatin emulsions immediately before spray-drying, then the desired hardening takes place. Since, in the process of spray-drying, considerable heat is used for drying the particles, some of the formaldehyde is lost by evaporation, but enough remains to harden the particles to the desired extent. A satisfactory proportion of formaldehyde to be added to the emulsion in this way is 1000 parts emulsion to l part 40% formaldehyde solution, and for convenience this may first be diluted with water to l0 parts. The ammonium alginate may be caused to become insoluble in water by adding to an ammoniacal ammonium alginate emulsion a small percentage of zinc oxide. This selves not only to render the spray-dried alignate powder insoluble in water but also to assist in whitening the emulsion. Spray-dried powder produced in this way from ammonium alginate is soluble in medium to strongly alkaline solutions, and these should be avoided when considering the choice of binder for coating the powder on to paper.

Even under the best spray-drying conditions, it is found that particle size varies fairly widely between rather less than 3 and rather more than l0 microns, though the bulk of the particles so obtained can be made between 3 and 6 microns. The large particles, however, tend to form a rather gritty coating on the paper or tend to be gritty here and there, and the coating process may be rendered more satisfactory in the following way.

The dried, hardened particles are dispersed as by Vigorous stirring in a suitable binder dissolved or mixed in water, as for example gelatin Vor ammonium `alginate or, in the case of casein prepared particles or gelatin prepared particles, gelatin or casein only. The amount of binder to particles, while not critical, appears to be of some importance and seems to be between 0.15 and 0.4 for a good grade of gelatin.

This dispersion is then passed through a simple colloid .mill of the kind which has two disc-like faces in juxtaposition and a few thousandths of an inch apart but with the faces moving at high speed with respect to each other, as for example might be obtained `by rotating a disc l0 in diameter `at about 6500 r.p.m. situated 2 to 3/1000 away from ya similar stationary disc into the centre of which the dispersion is fed. The dispersion passes between the stationary and rotating discs in such a way that the grosser particles tend either to be retained within the mill or to pass with the liquid layer through the mill and thereby become reduced to an average size of approximately 3-6 microns.

This dispersion is then coated and dried by heat on paper which may, if desired, have been prooed with a thin alkaline layer of ammonium alginate in water or gelatin in water or casein in water. In the ease of the ammonium alginate, a little zinc oxide is added to ensure insolubility when dry and in the case of casein and/or gelatin a little hexamethylenetetramine is added. During the drying process wherein heat is used, the hexamethylenetetramine generates within the mixture a little formaldehyde which then hardens the whole layer.

In the drying of the coating of the dispersion, the binder forming its continuous phase takes the form of a dry and hard lm, which is nevertheless pervious to fluid material and is suiciently friable to permit the colour-forming fluid material contained in the porous pressure-responsive sponge-like partie es to pass through such film, when the paper or other base web carrying the dried coating of the dispersion is subjected to writing pressure. In this way, the colour-forming fluid matcrial may be transferred to the surface of another sheet of paper which is in contact with the dispersion coating 'when the sheet carrying the latter is subjected to thc writing pressure. The presence of an acid substance in a coating ou the contacting surface of the underlying sheet causes the colourless dyestuff derivative in the fluid material expressed from the particles and passed through the pervious film to be converted to the coloured dyestuff, :so that the written characters made on the upper sheet when the latter is subjected to the writing pressure appear in copy form on the underlying, acid-coated sheet.

Any convenient method of coating these dispersions of sponge-like particles may be used, e.g. by means of rollers, doctor blades, air knives, or printing methods and the coated emulsion may then be dried by means of hot rollers, infra-red lamps or heaters with or without a strong blast of air either warm or cold.

EXAMPLE I Spray-dried emulsion An emulsion was made from the following:

Pts. by wt. Ammonium alginate (Collatex AX/RE)l 28 Finely-divided zinc oxide powder 41/2 Water 500 0.880 ammonia solution 50 1Ohtainah1e from Alginate Industries Ltd., Girvan, Scotland.

When the above had gone into a clear, pale brownish solution, the following solution was emnlsitied in:

Pts. by wt. Sextol phthalate 30 Dibutyl phthalate 30 p-Xylyl-leucauramine 3 The emulsiflcationwas continued until the oil-particles Were of the order of 5 microns in diameter, or less. The emulsion was then spray-dried, to give particles of 5-15 microns in diameter.

EXAMPLE II Spray-dried emulsion The following were prepared:

Pts. Iby wt. Sextol phthalate 20 Dibutyl phthalate 2O Phenyl-leucauramine 2 The emulsion was spray-dried to give particles up to 20 microns in diameter.

EXAMPLE III Binding solution The powder prepared in Example I was mixed with the following binder, passed through a high speed colloid mill to reduce the particle size to the order of 3-10 microns in diameter, and the resulting dispersion was coated on to s paper to give a coated weight of 4 lbs. per Double Crown ream (10 gms. per square metre).

Pts. by wt. Silver Stream gelatin 2 Titanium dioxide 21/2 Water 33 Fixanol C, 1% soln. 3 5% sodium carbonate solution 2 Spray-dried alginate colour-developing solution powder 12 EXAMPLE IV v Binding solution The spray-dried powder prepared as in Example II was mixed with a binder as follows:

Pts. by wt. Titanium dioxide 5 Potato starch 15 Cold water 50 40% formaldehyde solution 'l Boiling water 250 Anhydrous sodium carbonate 4 The titanium dioxide paste (I) was poured into the sodium carbonate solution (II) and when the starch had gelatinised the following was stirred in and the resultant dispersion passed through a high speed colloid mill arranged to reduce the particles to diameters in the range of 3-10 microns, the bulk of the particles having diameters of 3-6 microns:

Pts. by wt. Fixanol C, 1% solution 200 Spray-dried powder as in Ex. II 65 EXAMPLE V Acid coating mixture Pts. by wt.v Dextrin 40 Blanc xe 1150 Water 800 Pectin (240 grade)1 28 30% Fixanol C paste 15 1 Obtainable from British Drug Houses, Poole, Dorset.

Pts. by wt. Tannic acid 115 Dibutyl tartrate Finally, a solution of 16 parts by weight of phosphotungstic acid was stirred in. The composition was coated on to paper to give a coating of 5 lb. per Double Crown rearn (1l-l2 gms. per sq. metre).

In order that the inventiony may be readily understandable to Ithose skilled in the art, reference is made to the accompanying drawing in which:

Fig. 1 is a diagrammatic cross-section on an enlarged scale of one `formt of transfer sheet material;

Fig. 2 is a diagrammatic cross-section on an enlarged scale of one form of manifolding pack.

Fig. 1 shows a sheet of paper 10 carrying on a lsurface thereof a thin alkaline prooing layer 12. Over this layer 12, there is provided a coating comprising a continuous binder phase 14 and a discontinuous phase 16. The discontinuous phase 16 comprises a plurality of discrete, pressure-responsive, spray-dried sponge-like particles, which range'in particlesize from 3 microns to l0 microns, the bulk ofthe particles being between 3 and 6 microns in particle size. The particles have absorbed therein a colour-forming fluid material of the kind previously described in detail. The continuous binder phase 14 comprises a dry and hard but pervious film which is sufficiently friable to permit the colour-forming fluid material in the particles 16 to pass through the film or binder phase 14, when Writing pressure is applied to the sheet of Fig. l to express the fluid material from the particles 16.

Fig. 2 shows a manifolding pack comprising an uppermost, or A sheet, three intermediate, or B, sheets and a lowermost, or C, sheet. The A sheet is similar to the sheet illustrated in Fig. l. Each of the B sheets comprises a sheet of paper 18 carrying on the underside an alkaline proofing layer 12 and a coating of particles 16 in a binder 14, as does the sheet illustrated in Fig. l. The B Sheets also carry, on the upper side, a coating 20 of an acid substance, e.g. tannic acid. The C sheet comprises a sheet of paper 22 carrying on the upper side an acid coating 20 similar to that on the B sheets.

It may be mentioned that other forms of manifolding pack can be made with the transfer sheet material of the invention. For example, the pack can consist exclusively of B sheets, one A sheet and one or more B sheets or one or more B sheets and one C sheet.

I claim:

l. Transfer sheet material for use in manifolding, which comprises a base web and a substantially colourless coating carried upon a surface of the base web, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete particles of pressureresponsive sponge-like material having a particle size from about 3 to about l0 microns, and the sponge-like particles having absorbed therein a colour-forming fluid material containing a colourless derivative of a dyestuf adapted to be converted into the corresponding coloured dyestuff on reaction with an acid substance, the continuous phase of the coating consisting of a dry and hard but pervious film :sufficiently friable to permit the colour-forming fiuid material to pass therethrough, the pressure-responsive, sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to writing pressure, and thereby to be transferred to a copy sheet in contact with the coated surface of the transfer sheet material.

2. Transfer sheet material for use in manifolding in contact With a copy sheet, which transfer sheet material comprises a base web and a substantially colourless coating carried upon a surface of the base Web, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete spray-dried particles of pressure-responsive sponge-like material having a particle size substantially within the range of from about 3 to about 6 microns, and the sponge-like particles having absorbed therein a colour-forming fiuid material containing a colourless derivative of a dyestuff adapted to be converted into the corresponding coloured dyestuff on reaction with an acid substance carried by the copy sheet, the continuous phase of the coating consisting of a dry and hard but pervious film sufiiciently friable to permit the colour-forming fluid material to pass therethrough. the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable film when the transfer sheet material is subjected to Writing pressure, and thereby to be transferred to the copy sheet in contact with the coated surface of the transfer sheet material.

3. Transfer sheet material for use in manifolding in contact with a copy sheet, which transfer sheet material comprises a base web and a substantially colourless coating carried upon a surface of the base web, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete spray-dried particles of pressure-responsive sponge-like material selected from the group consisting of alginates, casein and gelatin and having a particle size from about 3 to about 10 microns, and the sponge-like particles having absorbed therein a colour-forming fluid material containing a colourless derivative of a dyestuff adapted to be converted into the corresponding coloured dyestuff on reaction with an acid substance carried by the copy sheet, the continuous phase of the coating consisting of a dry and hard but pervious film suficiently friable to permit the colour-forming fiuid material tcI pass therethrough, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fiuid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to writing pressure, and thereby to be transferred. to the copy sheet in contact with the coated surface of the transfer sheet material.

4. Transfer sheet material according to claim 3, Wherein the bulk of the sponge-like particles in the coating have a particle size from about 3 to about 6 microns.

5. Transfer sheet material for use in manifolding, which comprises a base web and a substantially colourless coating carried upon a surface of the base web, the coating being constituted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete water-insoluble particles of pressure-responsive sponge-like material formed by spray-drying a solution of a material selected from the group consisting of alginates, casein and gelatin in the presence of a hardening agent comprising formaldehyde, the particles of sponge-like material having a particle size from about 3 to about 10 microns, and the spongelike particles having absorbed therein a colour-forming fluid material containing a colourless derivative of a dyestut adapted to be converted into the corresponding coloured dyestuff on reaction with an acid substance, the continuous phase of the coating consisting of a dry and hard but pervious film sufiiciently friable to permit the colour-forming fluid material to pass therethrough, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to writing pressure, and thereby to be transferred to a copy sheet in contact with the coated surface of the transfer sheet material.

6. Transfer sheet material for use in manifolding, which comprises a base web and a substantially colourless coating carried upon a surface of the base web, the coating being constiulted by a continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete particles of pressure-responsive sponge-like material having a particle size from about 3 to about 10 microns, and the spongelike particles having absorbed therein a colour-forming fluid material containing a colourless dyestuf derivative selected from the group consisting of leucauramine and substituted leucauramines and adapted to be converted into the corresponding coloured dyestuff on reaction with an acid substance, the continuous phase of the coating consisting of a dry and hard but pervious film sufiiciently friable to permit the colour-forming fiuid material to pass therethrough, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to Writing pressure, and thereby to be transferred to a copy sheet in Contact with the coated surface of the transfer sheet material.

7. Transfer sheet material for use in manifolding, in contact with a copy sheet which carries a coating comprising an acid substance, which transfer sheet material comprises a base Web and a substantially colourless coating carried upon a surface of the base web, the coating being constituted by a continuous phase and a discon- 9 tinuous phase, the discontinuous phase of the coating comprising a plurality of discrete water-insoluble particles having a particle size substantially within the range of from about 3 to about 6 microns and comprising a pressure-responsive sponge-like material formed by spraydrying, in the presence of a hardening agent comprising formaldehyde, an aqueous solution containing a material selected from the group consisting of alginates, casein and gelatin, the sponge-like particles having absorbed therein an oily, colour-forming fluid material containing a colourless dyestuif derivative selected from the group consisting of leucauramines and substituted leucauramines and adapted to be converted into the corresponding coloured dyestuff on reaction with the acid substance, the continuous phase of the coating consisting of a dry and hard but pervious lm suciently friable to permit the colour-forming iluid material to pass therethrough, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit the fluid material to be expressed through the` friable lm when the transfer sheet material is subjected to writing pressure, and .thereby to be transferred to the copy sheet in contact with the coated surface of the transfer sheet material, the dyestuif derivative thereby reacting with the acid substance to form the coloured dyestuff in the form of Written characters upon the copy sheet.

8. Transfer sheet material for use in manifolding in contact with a copy sheet comprising a further portion of the same transfer sheet material, which comprises a base web, a substantially colourless first coating which includes an acid substance carried upon one surface of the base web and a substantially colourless second coating carried upon the other surface of the base web, the second coating being constituted by 'a continuous phase and a discontinuous phase, the discontinuous phase of the second coating comprising a plurality of discrete spray-dried particles of pressure-responsive sponge-like material selected from the group consisting of alginates, casein and gelatin and having a particle size from .about 3 to about l microns, and the sponge-like particles having absorbed therein a colour-forming fluid material containing a colourless derivative of a dyestuif adapted to be converted into the corresponding coloured dyestui on reaction with the yacid substance carried by the further portion of the transfer sheet material, the continuous phase of the second coating consisting of a dry and hard but pervious lm suciently friable to permit the colourforming uid material to pass therethrough, the pressureresponsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable lm when the transfer sheet material is subjected to Writing pressure, and thereby to be transferred to the acid-coated surface of the further portion of transfer sheet material in contact with the second coating of the first-mentioned portion of transfer sheet material.

9. A manifolding pack which comprises at least two portions of transfer sheet material, each portion cornprising a sheet of paper, at least all sheets except the lowermost sheet in the manifolding pack carrying on the lower surface thereof a substantially colourless coating, the coating being constituted by Ia continuous phase and a discontinuous phase, the discontinuous phase of the coating comprising a plurality of discrete spray-dried particles of a pressure-responsive sponge-like material selected from the ygroup consisting of alginates, casein and gelatin and having a particle size from about 3 to about l0 microns, and the sponge-like particles having absorbed therein :an oily, colour-forming uid material containing a colourless dyestut derivative selected from the group consisting of leucauramines and substituted leucauramines, the continuous phase of the coating consisting of a dry and hard but pervious iilm sufciently friable to permit the colour-forming iluid material to pass therethrough, and at least all sheets except the uppermost 10 sheet in the manifolding pack carrying on the upper surface thereof a coating including an. acid substance, the colourless dyestui derivative contained in the colourforming fluid material being adapted to be converted into the corresponding coloured dyestui on reaction with the acid substance present in the coating on the upper surface of the next underlying sheet of paper in the-manifolding pack, the pressure-responsive sponge-like particles being adapted normally to retain the colour-forming fluid material but to permit the fluid material to be expressed through the friable lm when the manifolding pack is subjected to writing pressure and thereby to be transferred to the aforesaid next underlying sheet of paper and to react there with the acid substance to form the coloured dyestuif in the form of visible written characters.

10. A manifolding pack according to claim 9, wherein each sheet of paper carrying on the lower surface thereof the coating constituted by the continuous and discontinuous phases is provided between such coating and the paper itself with an alkaline proofing layer which serves to prevent staining of the paper caused by undesired interaction of the dyestuff derivative and the acid substance.

11. A method of making transfer sheet material for use in manifolding, which comprises the steps of providing a base web, forming a substantially colourless emulsion comprising a colourless dyestui derivative and a material adapted to` form pressure-responsive, discrete sponge-like particles on spray-drying the emulsion, spraydrying the emulsion in the presence of a hardening agent to form a plurality of discrete particles of pressure-responsive sponge-like material having a particle size from about 3 to about 10 microns, the particles having absorbed therein a colour-forming fluid material containing the colourless dyestui derivative, which is adapted to be converted into the corresponding coloured dyestui on reaction with an acid substance, dispersing the particles in a binder therefor to form a dispersion having the binder as its continuous phase and the particles as its discontinuous phase and coating the dispersion on to one surface of the base web thereby to form a coating in which the binder forms a dry and hard but pervious lm sufiiciently friable to permit the colour-forming fluid material to pass therethrough and the pressure-responsive sponge-like particles are adapted normally to retain the colour-forming fluid material but to permit it to be expressed through the friable lm when the transfer sheet material is subjected to writing pressure and transferred to a copy sheet in contact with the coated surface of the transfer sheet material.

l2. A method of making transfer sheet material for Iuse in manifolding, which comprises the steps of providing a base web, forming an emulsion of a substantially colourless dyestuif derivative selected from the group consisting of leucauramine and substituted leucauramines dissolved in an oily substance with `a material selected from the group consisting of alginates, casein and gelatin, spraydrying the emulsion to form a plurality of discrete, pressure-responsive sponge-like particles of the selected material having a particle size from about 3 to about 10 microns, the sponge-like particles having absorbed therein a colour-forming fluid material containing the colourless dyestui derivative, dispersing the thus-formed particles in a binder to form a coatable dispersion of which the particles constitute the discontinuous phase and the binder constitutes the continuous phase, the continuous phase of the coating consisting of a dry and hard but pervious lm .sufficiently friable to permit the colour-forming uid material to pass therethrough, and coating the dispersion upon a surface of the base web, thereby to form a coating in which the pressure-responsive sponge-like particles are adapted normally to retain the colour-forming uid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to writing pressure, and transferred to a copy sheet in contact with the coated surface of the transfer sheet material, the colourless dyestuif derivative thereupon being converted into the corresponding coloured dyestuff on reaction with an acid substance present on the contacting surface of the copy sheet.

13. A method according to claim 11, whichV further comprises the step of applying' a'coating of the acid substance to the other surface of the base web.

14. A method according to claim 12, which further comprises the step of applying a coating comprising tannic acid to the other surface of the base web.

l5. A method of making a manifolding pack of transfer sheet material, Which comprises the steps of providing a base web, applying an alkaline proofing layer to a surface of the base web, forming a substantially colourless emulsion comprising a colourless dyestuf derivative selected from the group consisting of leucauraniine and substituted leucauramines dissolved in an oily substance with a material selected from the group consisting of yalginates, casein and gelatin, spray-drying the emulsion in the presence of a hardening agent comprising formaldehyde thereby to convert the emulsion into a plurality of discrete, water-insoluble, pressure-responsive sponge-like particles of the selected material having a particle size substantially within the range of from about 3 to about 6 microns, the sponge-like particles having absorbed therein a colour-forming uid material containing the colourless dyestulf derivative, dispersing the thus-formed Huidliolding particles in a binder material to form a dispersion of which the spray-dried particles constitute the discontinuous phase and the binder material constitutes the continuous phase, applying ya coating of the dispersion to a surface of the base webthereby to form a colourless coating in which the pressure-responsive sponge-like particles are contained ina dry and hard but pervious film suciently friable to permit the colour-forming uid material to pass therethrough and the particles are adapted normally to retain the colour-forming Huid material but to permit it to be expressed through the friable film, when the transfer sheet material is subjected to Writing pressure, and transferred to a copy sheet in contact with the coated surface of the transfer sheet material, applying to the other surface of the base web from that having the coating of the dispersion thereon a colourless coating of a material comprising tannic acid, and dividing the thus-coated base web into sheets and stacking the sheets into a manifolding pack in which the colourless dyestuff derivative carried in the coatingof the dispersion on cach sheet in the pack is adapted to be converted into the corresponding coloured dyestuff on reaction with the acid coating on the adjacent sheet in the pack.

References Cited in the tile of this patent UNLTED STATES PATENTS ivd-1-

Claims

1. TRANSFER SHEET MATERIAL FOR USE IN MANIFOLDING WHICH COMPRISES A BASE WEB AND A SUBSTANTIALLY COLOURLESS COATING CARRIED UPON A SURFACE OF THE BASE WEB, THE COATING BEING CONSTITUTED BY A CONTINUOUS PHASE OF THE COATING TINUOUS PHASE, THE DISCONTINUOUS PHASE OF THE COATING COMPRISING A PLURALITY OF DISCRETE PARTICLES OF PRESSURERESPONSIVE SPONGE-LIKE MATERIAL HAVING A PARTICLES ABOUT 3 TO ABOUT 10 MICRONS, AND THE SPONGE-LIKE PARTICLES HAVING ABSORBED THEREIN A COLOUR-FORMING FLUID MATERIAL CONTAINING A COLOURLESS DERIVATIVE OF A DYESTUFF ADAPTED ON BE CONVERTED INTO THE CORRESPONDING COLOURED DYESTUFF ON REACTION WITH AN ACID SUBSTANCE, THE CONTINUOUS PHASE OF THE COATING CONSISTING OF A DRY AND HARD BUT PREVIOUS FILM SUFFICIENTLY FRIABLE TO PERMIT THE COLOUR-FORMING FLUID MATERIAL TO PASS THERETHROUGH, THE PRESSURE-RESPONSIVE, SPONGE-LIKE PARTICLES BEING ADAPTED NORMALLY TO RETAIN THE COLOUR-FORMING FLUID MATERIAL BUT TO PERMIT IT TO BE EXPRESSED THROUGH THE FRIABLE FILM, WHEN THE TRANSFER SHEET MATERIAL IS SUBJECTED TO WRITING PRESSURE, AND THEREBY TO BE TRANSFERRED TO A COPY SHEET IN CONTACT WITH THE COATED SURFACE OF THE SHEET MATERIAL.