US3824118A - Process of producing ink sheet - Google Patents

Abstract

PROCESS FOR PRODUCING INK SHEET TO BE EMPLOYED AS THE INK SOURCE IN A STENCIL PRINTING PROCESS COMPRISING FORMING AN ORGANIC SOLVENT SOLUTION OF A HIGH MOLECULAR WEIGHT COMPOUND AND A COLORLESS LEUCO DYE WHICH IS CAPABLE OF FORMING A COLORED DYE UPON CONTACT WITH AN ACIDIC MATERIAL AND APPLYING SAID SOLUTION TO A SUPPORT.

Description

United States Patent 3,824,118 PROCESS OF PRODUCING INK SHEET Masayoshi Tsuboi, Yasushi Yano, and Yoshiaki Suzuki, Asaka, Japan, assignors to Fuji Photo Film Co., Ltd., Minami-ashigara, Kanagawa, Japan No Drawing. Continuation of abandoned application Ser. No. 840,501, July 9, 1969. This application Jan. 14, 1972, Ser. No. 218,008

Claims priority, application Japan, July 9, 1968,

Int. Cl. B41m 5/22 US. Cl. 117-362 2 Claims ABSTRACT OF THE DISCLOSURE Process for producing ink sheet to be employed as the ink source in a stencil printing process comprising forming an organic solvent solution of a high molecular weight compound and a colorless leuco dye which is capable of forming a colored dye upon contact with an acidic material and applying said solution to a support.

This is a continuation of application Ser. No. 840,501, filed July 9', 1969, now abandoned.

The present invention relates to a process of producing ink sheet. More particularly, it relates to a process of producing ink sheet containing leuco dyes.

In the case of ordinary stencil printing methods such as mimeographing, a colored ink is applied to one side of a stencil having openings therein while blank paper is supplied to the other side. The ink is forced through the openings of the stencil to form images on the blank paper corresponding to the openings of the stencil. However, since the ink is colored, it often stains not only the printing machine but the operators body or clothes. More over, it is difficult to transport either the ink or the printing machine with ease.

The inventors have discovered that stencil printing may be easily conducted by employing an ink sheet containing colorless leuco dyes on or in a support in combination with paper coated with an electron-accepting substance such as clay (hereinafter referred to as claycoated paper), thereby remedying the above-mentioned defects. The present invention relates to a process of producing such ink sheet.

It is accordingly an object of the present invention to provide a process of producing ink sheet which has superior printability.

Another object of this invention is to provide a process of producing ink sheet capable of producing images excellent in durability.

These objects are attained by adding to a leuco dye solution a high molecular weight compound having a melting point of from 45 C. to 210 C., and applying the mixture thus obtained to a support, as by soaking a support in the mixture.

As the leuco dyes to be employed in the products of the present invention, well-known chemical compounds which are normally colorless or light-colored, but which form colored dyes when they come into contact with solid acids can be used, such as benzoylleucomethylene blue, crystal violet lactone, malachite green lactone, Michlers hydrol, Michlers ketone, rhodamine B-lactame, acidrhodamine B-sultone, 3 dimethylamino 7 methylaminobuorane, 3-dimethylamino-7 diarylfluorane.

The solvent used to dissolve the leuco dye is preferably a solvent which is capable of dissolving more than 0.1% of the dye at room temperature, is free from offensive odor and has a boiling point of about 130 C. or more. The boiling point of the solvent should not equal or be less than the melting pint or softening point of the synthetic high molecular compound since the solvent would be vaporized, precipitating the leuco dyes when the solvent was heated for the purpose of melting the synthetic high molecular weight compound. Further, it often happens that, if a highly polar solvent is employed, the leuco dye will be slow in coloring or will fail to form a colored dye at all, even when in contact with an electron-accepting compound. It is preferable, therefore, that non-polar solvents be employed. The solvents preferably employed in this invention are aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, isopropylbenzene or ethylbenzene, chlorinated hydrocarbons such as chlorobenzene, trichlorobenzene or chlorinated diphenyl, or oxygen-containing solvents such as dibutyl ether, isobutyl ether, butyl acetate, amyl acetate, castor oil, or the like.

The synthetic high molecular weight compounds employed in this invention are those which are not soluble in either the above leuco dye solvents or in a mixture of the above solvents with up to 8% of an auxiliary solvent at a room temperature, but which are soluble to form a homogeneous solution at a temperature higher than their melting points or softening range in such solvents and whose melting points or softening ranges vary from 45 C. to 210 C. If the melting point or softening range is lower than 45 C., it becomes soluble, and if the melting point or softening range is more than 210 C., it becomes necessary to heat the synthetic high molecular weight compounds to such a high temperature in order to dissolve them that decomposition of the dye may take place.

As synthetic high molecular Weight compounds to be employed in the present invention may be mentioned polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polypropylene, vinyl chloride, polychorotrifluoroethylene, polytetrafluoroethylene, polyvinylpyrrolidone, ketone resins made from cyclohexanone and formalin, polybutadiene-1,2 (isotactic), polystyrene, synthetic rubber, polyamide resins made from dibasic aliphatic acids and polyamines and the like.

Among the above, polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polychlorotrifluoroethylene, polytetrafluoroethylene, ketone resins, synthetic rubber and polyamide resins are preferred. These synthetic high molecular weight compounds, even when heated, do not decompose to liberate acidic substances which cause the formation of leuco dyes.

When the synthetic high molecular weight compounds are mixed with the solution of solvent and leuco dyes, heated into a homogeneous solution and then cooled, they will be disolved to such an extent that the solution will not solidify. The most preferable synthetic high molecular weight compounds are those which, when they are dissolved in the leuco dye solution, heated and cooled, the surface of the leuco dye layer facing the air does not form a film, and moreover, in which the dye is separated into fine particles having a diameter of p. or less, and in which the softening range or melting point of the mixture is under C., whereby it is easily softened or melted. Such synthetic high molecular weight compounds comprise polyethylenes of low molecular weight (i.e., having an average molecular weight of 600'- 8,000); polyethylene-vinyl acetate resins having a vinyl acetate content of under 20% and a melt index above 50; polytrifiuorochloroethylenes having a pour point above 45 C. and an average molecular weight of LOGO-2,000; polyamide resins having amine value below 3; and ketone resins having an acid value below 1.

The dye solutions of the present invention may be prepared by any of the following methods:

(1) Dissolve the leuco dye in a solvent, add an auxiliary solvent if necessary, and mix the synthetic high molecular weight compound with the mixture while heating.

(2) Heat the leuco dye, the synthetic high molecular compound and an organic solvent into a homogeneous solution, adding subsidiary solvent if necessary.

(3) Dissolve a leuco dye in a solvent, heat this solution to a temperature below the softening point or melting point of the synthetic high molecular weight compound. Further add the synthetic high molecular Weight compound, which is melted by heating at a temperature above the melting point, while stirring vigorously. The system becomes homogeneous, consisting of minutely dispersed particles of the synthetic high molecular weight compound in the solution.

Of these methods, method (1) is the simplest and most preferred.

The leuco ink, prepared as above, is then applied to a support, under either heating or cooling, to produce the ink sheet of this invention.

The preferred proportions of each component contained in 100 gr. of the ink of this invention are set forth below.

The leuco dyes are present in the range of from 0.1 wt. percent to 20 wt. percent of the ink composition. Amounts of 0.4 Wt. percent or above are preferred where the coloring ability of the particular leuco dye is low. Further, in general, it is preferred to employ amounts of leuco dyes of about wt. percent or less.

The synthetic high molecular weight compound should be present in an amount of about 2 wt. percent or more, based upon the weight of leuco ink, in order to plasticize the ink and increase its viscosity. However, it should not be present in an amount greater than about 28 wt. percent to obtain good printability. The synthetic high molecular weight compound can be partially replaced with waxes, oils, fats, or fine powdered substances such as starch or powdered cellulose. The proportion of synthetic high molecular weight compound present has an important bearing on the undesirable stickiness and the printability of the ink sheet. For the purpose of producing ink sheet of good printability and reduced stickiness, it is particularly preferred that the proportion of the high molecular weight compound is between about 6 wt. percent and wt. percent.

The remainder of the ink composition comprises the leuco dye solvent plus, if desired, an auxiliary solvent. Since, in many cases, the leuco dye solvents dye badly after the commercially available stencil paper for typewriting, it is preferred to employ as little of such solvents as possible, so that flowing of the leuco dye solvents does not take place. As auxiliary solvents may be mentioned liquid paraffin, gasoline, soya bean oil, kerosene, silicone oil and the like. Especially, liquid paraffin is an excellent auxiliary solvent and is particularly preferred since it decreases the temperature dependence of the viscosity of the ink and is odorless. Liquid paraffin also enhances the stripping of the protective sheet from the ink layer.

Two or more leuco dyes, solvents, and/or synthetic high molecular weight compounds may be employed. Finely powdered substances solid at room temperature, paraflin, waxes, fats and oils, and/or a small quantity of coloring matter or pigment for improved appearance may also be added.

As the ink sheet support, a sheet-like substance which is relatively unaffected by either the leuco dye solvents or the auxiliary solvents is preferable. Further, a flexible sheet which is resistant to temperatures of about 100 C. is preferable. Examples of such materials are aluminum foil, non-woven fabrics, paper containing no acidic substances, cellophane sheet, polyethylene sheet, polyvinyl chloride sheet, polyester sheet, cellulose derivative sheet, poly(vinylchloridevinylidene) sheet, polypropylene sheet, polystyrene sheet, paperlike polystyrene sheet, or laminated sheet of the above-mentioned polymer sheet and paper, laminated sheet of the aluminum foil and paper, or cloth, or laminated sheet of cloth and paper. Also, polymer sheet or aluminum foil laminated with such porous layers as paper, non-woven fabric, or thin, spongelike sheet may be used as supports.

The amount of leuco dye to be applied to the support varies according to the number of copies to be made. For example, by means of an ink sheet coated to a thickness of 0.1 mm. with an ink containing 2.0 g. of leuco dyes in g. of the ink, more than 300 copies can be obtained.

The high molecular compounds contained in the ink sheet of this invention form, at room temperature, dispersed particles, uniformly separated from each other in the solution so that stickiness to the touch is reduced. Moreover, by the use of this ink sheet, unevenness of printing is avoided since the leuco dye moves evenly to the paper to be printed, due to the synthetic high molecular weight compounds which are dispersed uniformly on the sheet. In addition, the printed image is protected by the synthetic high molecular weight compounds, which are partly dissolved in the leuco dye solution at room temperature, thus increasing the durability of the image. When materials such as waX, oils, fats or mineral oil were used, previously they sometimes formed large crystals over a period of time, and these coarse particles in the ink layer would spoil the printability. In the case of the ink sheet containing synthetic high molecular weight compounds obtained by means of this invention, however, fine particles of the synthetic high molecular weight compounds are dispersed uniformly, no coarse particles are being formed with the passage of time, and at the same time the stickiness of the ink sheet is remarkably decreased. Moreover, the synthetic high molecular weight compounds condense foams between the ink sheet and the stencil during the printing and remarkably improve the printability by doing away with typographical broken ness or defacement.

EXAMPLE I 0.1 g. Crystalviolet lactone is dissolved in 6 g. of chlorinated diphenyl. To this solution is added 1.0 g. of liquid parafiin, 2.0 g. of polyethylene having an average molecular weight of 2,000 and a softening point of 107 C., and 1.0 g. of paratfin having a melting point of 62 C.- 64 C. The mixture is then heated at l20 C. to obtain a uniform, citrine and transparent solution. This solution is applied to the cellophane side of cellophane laminated paper to a thickness of g./m. Then a sheet of tissue paper is attached to it as a protective sheet, thus producing the ink sheet. The tissue paper is taken off, a stencil is put on the ink layer, and copies are made on clay-coated paper with a handprinting mimeograph. During the printing, hands and clothes are not stained. The ink layer, cooled to room temperature, is colorless. It contains solid minute dispersed particles of deposited polymer and paraflin. Stickiness is minimal.

EXAMPLE II 0.45 g. of Benzoylleucomethylene blue is dissolved in 8.55 g. of chlorinated diphenyl and the solution heated to 75 C. Then 1.2 g. of polytrifiuorochloroethylene (trade name: Daifloil 100, mobil temperature 50-65 C., manufactured by Osaka Kinzoku Kogyo Kaisha Ltd.) is heated to 75 C. The above-mentioned heated solution of benzoylleucomyethylene blue is then added to the heated polymer and the mixture stirred until a uniform, transparent solution is obtained. This solution is cooled to room temperature to produce an opaque paste. This paste is then coated on the aluminum foil side of a laminated aluminum foil sheet and covered with a protective polypropylene film to produce the ink sheet. This ink sheet is only slightly sticky, its color is citrine, and the protective sheet can be easily peeled off. By printing in the same way as in Example I, clear blue prints are obtained.

EXAMPLE III 1.0 g. of rhodamine ,e-lactam is dissolved in 7.8 g. of chlorinated diphenyl. To this solution is added 1.2 g. of

ketone resin (trade name: Hilac 110, manufactured by Hitachi Kasei Kogyo Kaisha Ltd.). Then this mixture is heated at 130 C. to obtain a transparent solution. After cooling to room temperature, this solution is coated on polyester film to a thickness of 80 g./m. and covered with polyvinylchloride film as the protective sheet to obtain the ink sheet. This ink sheet is easy to handle, and the proective sheet is easily peeled off. The protective sheet taken off, the ink layer is placed upon the stencil prepared by means of the electrostatic facsimile process (trade name: Stencil paper for Gestfax ES 390) and stencil printed on paper coated with Japanese acid clay by means of multigraph. Thus a clear red printed paper is obtained. The printing is satisfactorily conducted both at 5 C. and at 40 C. Almost no staining of hands and clothes occurs during the printing. 200 sheets of printed paper are obtainable.

EXAMPLE IV 1.0 g. of malachite green lactone is dissolved in 22 g. of butyl acetate. 15.0 g. of chlorinated triphenyl is then added gradually while heating. To this, 15.0 g. of liquid paraffin and 3.2 g. of ethylenevinyl acetate copolymer (trade name: Evaflex #420, manufactured by Mitsui Polychemical Co. Ltd.) is added and the mixture heated at 100 C. A nearly transparent solution is obtained. This hot solution is coated on the cellophane side of cellophane laminated paper to obtain an ink layer of 160 g./m. in thickness. Poly(vinyl-vinylidene cholride) film is put over it as a protective sheet and thus an ink sheet is obtained. Using this ink sheet and a stencil prepared by means of a thermographic process (trade name: Risofax, manufactured by Riso Kagaku Kaisha Ltd.), a clear blue-green print is obtained by stenciling with an electrorotary mimeograph on paper coated with attapulgite clay. This ink sheet is colorless and only slightly sticky. At a speed of 80 sheets per minute and at a temperature of 9 C.35 C., over 450 sheets of prints are obtainable.

EXAMPLE V 2.0 g. of crystalviolet lactone and 2.4 g. of leucomethylene blue are dissolved in a mixed solvent of 70.6 g. of chlorinated diphenyl and 13.0 g. of kerosene, 14.5 g. of polyamide resin (trade name: Hitamid 502, manufactured by Hitachi Kasei Kogyo Kaisha Ltd.) is added to it. The mixture is then heated to 120 C. to obtain a clear solution. After being cooled to about 40 C., this solution is applied to a polyester film in the thickness of 60 g./m. Glassine paper is put over it as a protective sheet, and the ink sheet is obtained. This ink sheet, light creamy in color, is only slightly sticky, and the proective sheet is easily peeled off. The protective sheet taken off, the ink sheet is afiixed to the frame of a mimeograph together with a wax stencil. By printing with a clean roller, clear, blue prints are obtained. Printing is successful at both 5 C. and 40 C.

EXAMPLE VI 1.0 g. of 3-diethylamino-7-methylaminofiuoran is dissolved in 20.0 g. of chlorinated diphenyl. To this solution is added 50.0 g. of liquid parafiin, 13.0 g. of polyethylene of average molecular weight 5,000, and the mixture heated to 120 C. to obtain a clear solution. Then this solution is cooled to about 60 C., applied in a thickness of about 100 g./m. to the non-woven fabric side of a cellophane sheet laminated with non-Woven cellulose fabric. Aluminum foil is put over it as a protective sheet, and thus the ink sheet is produced. The protective sheet is taken off, White Mirya stencil (manufactured by Horii Toshado Kaisha Ltd.) put over the ink sheet, and printing performed on paper coated with bentonite and magnesium oxide to produce black prints. More than 300 prints are obtainable with this ink sheet. The ink sheet is colorless and no staining of hands or clothes is experienced. Handling is easy because the ink sheet is semi-dry.

With regard to the above examples, Daifloil is a polytrifluorochloroethylene having a degree of polymerization of 1,300 and a softening range of 50 to 65 C.; Hilac 110 is a copolymer prepared from cyclohexanone and formaldehyde and having a softening range of 110 to 130 C.; Evafiex 420 is an ethylene-vinyl acetate copolymer containing 18% vinyl acetate and having a softening point of 99 C.; and Hitamid 502 is a copolymer prepared from an aliphatic acid and a polyamine and having a softening range of to C.

What we claim is:

1. A process for producing an ink sheet useful in a stenciling process, said sheet comprising a support carrying a solution of a colorless ink coated thereon, said solution being of a viscosity suitable for use as an ink in a stenciling process, which comprises the steps of (a) dissolving in a non-polar organic solvent selected from the group consisting essentially of aromatic hydrocarbons, aromatic chlorinated hydrocarbons and oxygen-containing solvents, a substantially colorless leuco ink, in an amount of from about 0.1 to about 20.0%, by weight, of the ink composition, said ink capable of forming a colored ink when coming in contact with an electron-accepting solid acidic material,

(b) mixing with the solution thus formed, an organic synthetic high molecular weight compound selected from the group consisting of chlorinated polyethylene, vinyl chloride, polyvinyl pyrrolidone, isotactic polybutadiene-1,2 and polystyrene, having a melting or softening point ranging from about 45 C. to about 210 C., said compound being present in an amount ranging from about 2.0% to about 28.0% by weight, of the leuco ink, and said compound being insoluble in said solvent at room temperature,

(c) heating the mixture thus formed to a temperature higher than the melting or softening point of the organic synthetic high molecular weight compound, thereby forming a homogeneous solution,

(d) cooling the solution thus formed to a temperature lower than the melting or softening point of said organic synthetic high molecular weight compound, thereby forming a dispersion of said organic synthetic high molecular weight compound, and

(e) applying the resulting dispersion to a suitable sup port,

said resulting solution maintained on said support in a non-solidified state of a viscosity suitable for use as an ink in a stenciling process, and

said high molecular weight compound and said dye capable of being transferred when said ink sheet is contacted with a receptive sheet.

2. A process for producing an ink sheet useful in a stenciling process, said sheet comprising a support carrying a solution of a colorless ink coated thereon, said solution being of a viscosity suitable for use as an ink in a stenciling process, which comprises the steps of:

(a) dissolving in a non-polar organic solvent selected from the group consisting essentially of aromatic hydrocarbons, aromatic chlorinated hydrocarbons and oxygen-containing solvents, a substantially colorless leuco ink, in an amount of from about 0.1 to about 20.0% by weight, of the ink composition, said ink capable of forming a colored ink when coming in con tact with an electron-accepting solid acidic material,

(b) mixing the solution thus formed, an organic synthetic high molecular weight, compound selected from the group consisting of polyethylene, ethylenevinyl acetate copolymer, polypropylene, polychlorotrifiuoroethylene, polytetrafiuoroethylene, ketone resins, synthetic rubber, and polyamide resins,

(c) heating the mixture thus formed to a temperature higher than the melting or softening point of the organic synthetic high molecular weight compound, thereby forming a homogeneous solution,

((1) cooling the solution thus formed to a temperature lower than the melting or softening point of said organic synthetic high molecular weight compound, thereby forming a dispersion of said oragnic synthetic high molecular weight compound, and (e) applying the resulting dispersion to a suitable supsaid resulting solution maintained on said support in a non-solidified state of a viscosity suitable for use as an ink in a stenciling process, and said high molecular weight compound and said References Cited UNITED STATES PATENTS 3,079,351 2/1963 Staneslow et a1. 11736.2 3,418,148 12/1968 Barz 117-36.1

MURRAY KATZ, Primary Examiner US. Cl. X.R.

dye capable of being transferred when said ink 10 1l7l38.8 UA, 155 UA, 132 C sheet is contacted with a receptive sheet.

UNITED STATES PATENT OFFICE CERTIFICATE OF QQRRECTION Patent No. 824:, 118 Dat d July 16, 1974 Invent0r(s) Masayoshi TSUBOI et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE CLAIMS:

Column 6, claim 2, line 64 following "mixing" insert with Signed end sealed this 11th day of March 1.975.

(SEAL) Attest:

a C. MARSHALL DANN RUTH C r-IASON Commissioner of Patents. Attestlng Officer and Trademarks