US2696168A - Method of printing - Google Patents

Description

United States PatentO" 2,696,168 METHOD OF PRINTING No Drawing. Application March 28, 1952, Serial No. 279,257

5 Claims. (Cl. 101-416) assignor to Fredk H. N. Y., a corporation Ly present invention relates to the art of printing and provides an improved method whereby freshly printed material may immediately be freely handled without danger of smearing, even before the ink has dried, thus avoiding the necessity of forced drying of the ink.

According to conventional practice, where it is necessary that the printed material be substantially immediately dried after printing, a volatile solvent is included in the printing ink and, following printing, heat is applied to the printed material to drive off the volatile solvent and leave the ink substantially dry and bonded to the This procedure has serious disadvantages.

Two types of printing processes which utilize this method of heating to hasten the drying of the ink are the letterpress process, in accordance with which the printing surface is raised, and the offset or lithographic process, in accordance with which the printing surface is planographic. In order to hasten the drying of the ink so as to obtain the desired printing speed in processes of these types, it is usually necessary that the printed material be subjected to temperatures so high as to tend to the paper, usually of the order of 300 frequently leads to production delays due to the breaking of the web and is also costly due to the amount of fuel required for heating to such high temperatures.

A further difficulty which has been experienced where it has been attempted to hasten the drying of the ink by heating is the necessity of using volatile solvents in the ink. Such solvents must be sufiiciently volatile to be driven off by the applied heat, yet having an evaporatlon rate low enough to keep the ink wet on the distributing and printing rollers or plates so that the paper will not be picked or ripped by adhering to the partially dried ink on the printing surfaces. This latter condition has necessitated a compromise between ink solvents which evaporate sufficiently satisfactorily and those rapidly to effect an optimum sible heating temperature.

I have discovered that, contrary to what would be expected, freshly printed wet ink films may be effectively sealed in and bound to the paper, without harming the ink film in any wa by applying over the wet ink film immediately after printing, a fast drying film-forming solution, such as hereinafter described. By selecting a suitable film-forming solution, a dry protective film is immediately formed over the wet ink and the print may be handled as though the ink were completely dry.

This film or coating is applied to the wet printed surface by means of a contacting surface as by a plate, smooth roller or blanket or a revolving cylinder, such as fully hereinafter described.

which evaporate sufficiently drying rate at the permislar operation will be dictated primarily by the required rate of drying of the film, the method of application to be employed, and costs. A further requirement is that the material be suitable for application as a thin film.

The film-forming material, hereinafter referred to as the resin constituent, may be any one, or a compatible mixture of, a Wide variety of resins or plastics, soluble or dispersible in a suitable solvent and capable of forming a continuous thin film which is transparent or nearly so, for instance, those of the cellulose derivative type, such as, cellulose acetate, ethyl cellulose, or carboxymethyl cellulose; of the protein type, such as ammonium casemate;

slowly to permit the ,ink to print "ice '2 rosin and rosin derivatives; shellac; maleic resins; latices, such as emulsions of vinyl resins, polystyrene, polyacrylates, polymethacrylates; modified phenolics; other synthetic, natural or fossil resins; or sodium silicate.

As a solvent constituent I may use any of the known large group of low boiling volatile solvents capable of dissolving or dispersing the particular resin constituent selected, or compatible mixtures of such solvents, for instance, water; alcohols, such as methanol, ethanol, or the propyl alcohols; mixtures of such alcohol and water; others, such as mono-alkyl glycol ethers; esters, such as ethyl acetate; ketones, such as methyl ethyl ketone; toluene, naphtha, or other volatile aliphatic or aromatic hydrocarbons.

As the method of application involves contact between the applicator and the wet print, it is essential that no solvent be used in the coating solution which is a solvent for the vehicle of the ink. Otherwise the solvent may dissolve the printed ink and cause it to mix with the coating composition and be transferred to the surface by which the coating solution is being applied.

It has previously been proposed to protect printed matter by applying thereto a protective film. However, to my knowledge, such films have invariably been applied after the ink has first been permitted to dry. Such coatings are usually applied to labels or magazine covers to protect the ink from scufiing when they are rubbed against each other and to enhance the gloss of the printed matter. My present invention is distinguished from such prior practice by the fact that the protective film is applied while the ink is still Wet, and is adapted to permit greater printing speed, as distinguished from affording protection to the finished printed matter.

Advantageously the protective film is applied to the moving printed web of paper while the latter is passing through the press. By this procedure, the protective film has been found to cover and protect the Wet printed ink so well that the paper may be turned over and immediately printed on the reverse side with no transfer of ink to the guide bars, guide rollers, or second impression cylinders of the press and can be passed through folders with no marring of the printed surface.

The finished product is delivered at the end of the press, ready for use without further treatment.

It will be understood that the solvent used in the protective coating solution should be sufliciently volatile so that the coating will immediately dry with little or no heating.

Where the press is operated at moderate speeds, no heating whatever is ordinariy required in order to obtain the necessary drying rate. However, at high speeds, some heating may be used with advantage. But, in no case has it been found necessary to heat the printed web to a temperature higher than about 250 F. in order to obtain instantaneous drying of the protective film. The term instantaneous drying, will be understood to mean that the film is dried by exposures of the order of a few seconds or less.

It is an advantage of the present invention that the printing ink need not contain volatile solvents. There may be used as the vehicle of the printing ink any of the common vehicles now used for that purpose such as vegetable, or mineral oils, with or Without resins dispersed therein. By avoiding the necessity for forced drying the ink, the use of volatile ink solvents may be eliminated and difficulties due to the partially drying of the ink on the rollers and plates of the press avoided.

As previously noted, the protective coating is applied by means of contacting surfaces, such, for instance, as a plate, roller or blanket, composed either of rubber, plastic, or metal and adapted to apply a solid continuous film over the wet printed surface. The printing process may be by aniline, letterpress or offset printing methods, with necessary modifications in the distribution system of the press to apply such coatings containing highly volatile solvents, as will be readily understood by the printing art.

The application of the coating solution by means of a roller will, of course, involve the application of the coating solution to the roller and may also involve the distribution of the coating solution over the roller in much the manner that ink is applied to and distributed over such rollers. However, by reason of the low viscosity of the coating solution, distribution means may be reduced to a minimum. The coating composition may be applied to the wet printed surface by a roller of the type normally used in applying the ink and which is usually of rubber. The roller may be caused to revolve in contact with a body of the coating solution and the excess by means of a metering roll revolving in the coating solution. By either of these methods of application, the protective film has been found to cover the wet printed ink so well that the paper may be turned over and immediately printed on the opposite side with no transfer of the printed ink film to the guide bars, guide rollers or second impression cylinders of the press. And if a folder is used on the delivery end of the press, there is no marring of the printed surface by the folder.

It will be understood that, in ordinary printing of the type described, where a heavy viscous ink is normally used, it is usually necessary to pass the ink along a series of rolls in order to get uniform distribution. This has materially limited the permissible volatility of the solvent used in the ink. However, in applying my protective coating by the roller method, the distribution requirements are minimized and accordingly highly volatile solvents may be used in the coating, so that the coating will immediately dry, without heating or with only a mild heatmg.

That aspect of my invention wherein the protective coating is applied by means of a plate or roller will be illustrated by the following specific examples:

Example I A coating solution of the following composition:

Per cent Alcohol 8O Ethylcellulose (low viscosity) 20 136 was applied by means of a rubber plate to a web of wet print of a petroleum base ink, drying of the coating being expedited by a current of air. By this method, the wet ink was sulficiently protected so it could not be smeared, or rubbed and the gloss and color depth of the ink was materially improved.

Example 11 A coating solution of the following composition:

Per cent Ammonium caseinate (dry) 14 Water 86 was applied to a moving web of wet print, as described in Example I, and by the method there described. Satisfactory protection for the wet ink against smearing or rubbing was obtaine As previously noted, the protective film may be applied to the wet printed surface by means of a gravure cylinder, that is, a printing cylinder Where the impression to be transferred to paper is depressed in the cylinder surface as by etching or knurling. In using gravure cylinders, the protective film is applied to the wet print in substantially the same manner as where the rubber rollers are used and with the same advantageous results. Also the same coating solution is generally equally applicable to either process. In either type of operation it has been found especially advantageous to use, as the resin constituent of the coating solution, either a cellulose derivative, or a protein, a rosin derivative, shellac, a maleic adduct resin or a latex, such as previously noted, or a compatible mix- That aspect of my invention in which the coating solution is applied to a web of Wet print by means of a gravure cylinder will be specifically illustrated by the following examples.

Example III The coating composition of Example I Was applied by means of a gravure cylinder over a Web of wet print of thereon is still Wet, in direct, non-wiping contact with a solid contact surface wet with a thin film of the solution, the solvent constituent of the solution being volatile and the solution being a non-solvent for the wet ink.

2. Process of claim 1 in which a web of wet print, while passing at high speed through a printing press is passed in direct, non-wiping contact with the surface of a roller wet with the film-forming coating solution.

3. The process of claim 1 in which the film-forming material is a resin.

4. The process of claim 1 in which the film-forming material is ethyl cellulose.

5. The process of claim 1 in which the film-forming material is ammonium caseinate.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Process of Drying Sheets Between Impressions, from Encyclopodie der Graphischen Kunste, Woldow, 1884. Article Fahrenbendrucke Zu Trocknen, page 259, 2nd col. (Translation available in Div. 17.)

Claims (1)

1. METHOD OF PROTECTING WET INK FILMS ON PRINTED SURFACES WHICH COMPRISES APPLYING TO THE SURFACE, OVER THE WET INK, A CONTINUOUS, THIN FILM OF A TRANSPARENT FILMFORMING COATING SOLUTION BY PASSING THE PRINTED SURFACE, WHILE THE INK THEREON IS STILL WET, IN DIRECT, NON-WIPING CONTACT WITH A SOLID CONTACT SURFACE WET WITH A THIN FILM OF THE SOLUTION, THE SOLVENT CONSTITUENT OF THE SOLUTION BEING VOLATILE AND THE SOLUTION BEING A NON-SOLVENT FOR THE WET INK.