US2602072A - Finishing varnish for application over lithographic ink - Google Patents

Description

Patented July 1, 1952 FINISHING VARNISH FOR APPLICATION OVER LITHOGRAPHIC INK Paul W. Greubel, Great Neck, N. Y assignor to American Can Company, New York, N. Y a corporation of New Jersey No Drawing. Application April 8, 1948,

Serial No. 19,874

22 Claims. (01. zen-29.2)

The present invention relates generally to finishing varnishes for lithographic inks and more particularly to novel improvements in those finishing varnishes which are applied over wet lithographic inks printed upon various web or sheet materials especially sheet metal, such as tin plate, terne plate, enameled sheet metal, etc. and to a method of wet ink varnishing in which the ink pigment is flocculated on application of the varnish to a freshly lithographed sheet, and thereby preventing bleeding or ridging of the ink.

For many years it has been the practice, for example, in the decorated or lithographed sheet metal container art, to pass freshly lithographed metal sheets thru ovens for the purpose of drying the lithographic ink printed thereon before applying the finishing varnish which constitutes the final coating operation. -Finishing varnishes are used to protect the lithographed surface and to improve its appearance by producing a hard, protective and glossy finish. g I

Later, attemptswere made to economize these operations by applying the wetfinishin varnish directly over the wet ink and then passing the web or sheet thus coated thru the drying oven, thus drying both the wet ink and the 'wet varnish coats in a single operation. This process is known in the art/as wet varnishing or wet ink varnishing. It saves considerable time and laborand would have many advantages if it were completely successful. However, the results obtained are unpredictable and havebeen far from satisfactorily uniform. It has been partially successful with only a relatively few finishing varnish formulations. In addition to restricting the use of many desirable and commercially required varnish formulations, the main difficulty has been inferior appearance such. as lack of sharpness and lack of gloss in the finished lithographed product. More specifically, the inferior appearance is dueto the bleeding or running of the ink under the leveling action of the varnish coating, the ink flowing away from the printed areas at the edges; also the ink fiows into macroscopic ridges or waves in the more solid areas thereby producing a mottled and/or raised effect.

After extensive observations, experiments and tests conducted over a considerable period of time, I discovered the causes or reasons for these undesirable results. I found that they are due to certain physico-chemical phenomena'similar to those which occur in the process of detergency.

By experimenting with a great inany, different 2 mixing the respective inks and varnishes and observing them'microscopicallyil found that in all cases of failures there occurred ,a local movement of the ink film similar in action to that of detergency or washing away and that the pig ment particles of theink film were always tie fioccuated. Close examinationrevealed that the two undesirable phenomena, i. e. bleeding or runningand ridging or waving are the same in principle, each being the result of a disturbance or movement of the ink as levelling of the. finishing varnish occurs. I also found" that in all cases where bleeding and ridging did not occur, the pig;

ment was always fio'cculated and where these un-' V desirable phenomena did occur. the pigmentwas always inastate ofdeflo cculation. f I 1 j Upon discovering the reason or cause of the trouble, 1. e. defiocculation of the ink pigment,

I started the search for a proper remedy. It

occurred to me that the diflicultiescould probably be overcome by searching out and utilizing lithographic inks and finishing'varnishes'which are completely or at least substantially' immiscible. I soon discovered that this approach to the solution of the problem was impracticalin view of the present state of the art. The film forming materials used in both inks and varnishes are usually essentially of the same general nature; i. e. both'may be made from drying oils with or without resins or the finishing varnish usually contains a solvent which is also a solvent'for the ink vehicle. Therefore, this method of ap proach would be successful only with very few and very carefully selected materials. This would severely limit the choice of materials .from which the inks and finishing varnishes could be made. Since commercial requirements make itimpera tive to have as wide a range of .materials available as possible for use in this process, I searched for other means of solving the problem.

Next I thought of producing a flocculated ink I by incorporating a flocculating agent in the ink during its manufacture. This method also proved impractical because an ink strongly flocculated before printing possesses certain undesirable characteristics which make it'difficult to handle in the printing presses. I I

I then discovered that all the desirable results from a commercial use standpoint'can be best secured by the incorporation of a flocculating agent or a combination of fiocculants in a finishing varnish which on contact with the wet lithographic ink positively induces a strongly .flocculated structure in the ink pigment and prevents bleeding orridging of the ink when the varnish is applied over the wet ink. a I 1 Water and certain water solubleorganicsub TE T ori ice fined by their common physical characteristics. 7

They must all be liquids. They must all be substantially immiscible or at least of a very low order of miscibility with the ink vehicle-finishing varnish system. The term immiscible is used in a relative sense. They must all be polar compounds.

Polar compounds are those in which the force uniting the atoms in the chemical bond is the electrostatic attraction between oppositely charged particles. This electrostatic attraction is present in ionizable compounds and in compounds having electrostatic dissymmetry or oppositely charged groups in their spatial structure.

Immiscible liquids are those wherein one liquid will not blend or dissolve in another or will blend or dissolve only to a very limited degree, such that when they are poured together two distinct or separate layers or phases result. Absolute immiscibllity may be said to be non-existent and may be assumed to be useless as a flocculant since this would imply absolute immiscibility with the other liquids in the wet varnish system. Immiscible in connection with the present invention refers to a relatively low order of miscibility in the ink vehicle-finishing varnish system. The force of fiuocculation induced by immiscible liquids decreases as miscibility increases. I

And finally these materials must be incorporated in the finishing varnish in certain percentages by weight, which vary with difierent vare nish compositions and ink compositions, which percentages will be effective in inducing immediate flocculation of the pigment in the lithographic ink.

While immiscibility or substantial immiscibility of the fiocculating liquids is a necessary characteristic I discovered that because of the low order of miscibility of these compounds this desirable characteristic is accompanied by the phenomenon of sometimes establishing a twophase system in the finishing varnish. Therefore it is sometimes necessary that the immiscible flocculant be rendered sufiiciently accessible to the lithographic pigment so that it can come into intimate contact with said pigment whereby it increases the interfacial tension between the pigment surface and ink vehicle, which will result in immediate, strong flocculation of the lithographic ink pigment. I solved this problem by introducing a coupling agent or mutual solvent into the varnish composition. The coupling agent or mutual solvent must be miscible with the ink vehicle, the varnish vehicle and the fiocculant. The function of the coupling agent or mutual solvent is to maintain the varnishfiocculant mixture in a single continuous phase before application of the varnish to the inked surface and further to continue to maintain a single liquid phase when such mixture is applied to the wet ink so that the flocculant can readily penetrate the ink vehicle in order to gain access to the ink pigment. Where a certa n 4 solvent already in the varnish composition is capable of functioning as a coupling agent, no additional or a lesser amount of coupling agent is required. 1- I Among the fiocculants which I have found to be satisfactory are:

(1) Water (2) Alkanols of from one to three carbon atoms inclusive such as methanol, ethanol, isopropanol, normal propanol (3) Lacticacid (commercial U. S. P. grade) (4) Formamide (5) Dihydric alcohols of from two to four carbon atoms inclusive, such as: Ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, etc.

(6) Glycerol For the purpose of the present invention I prefor to emphasize water.

All of the flocculants which I found to he sat-- isfactory including those specifically mentioned come under the definition relatively oil immiscible, water soluble polar liquids. The word oil in-this definition, for the purpose of my invention, means the water insoluble oil, resin or other film forming materials constituting the vehicle of lithographic inks. My extensive experiments and tests conclusively show that no material or compound which does not come under this definition functions as a satisfactory flocculant and conversely all materials or'compounds which do answer this definition are good flocculants. Water falls under the classification of relatively oil immiscible water soluble polar liquids.

Water, with or without coupling agents, is incorporated into the finishing varnish formulation, in such percentages by weight of complete finishing varnish as will result in'the required or optimum flocculation in the wet ink film.

The percentage of flocculant required varies in accordance with the particular varnish composition in which it is to be embodied. It varies in accordance with the fiocculating force or ability of the particular fiocculant itself. And it may vary in accordance with the particular lithographic ink pigment which it is to fiocculate. For example, I have found that milori blue requires a higher percentage of fiocculant than any other lithographic ink pigment, and that when bleeding and ridging of this pigment is stopped, bleeding and ridging of all other pigment also is controlled. I

The required percentage of flocculant in each commercial formulation of finishing varnish for stopping either bleeding or ridging can be readily determined by the following methods:

Bleeding The method consists of preparing several aliquots of a given varnish, keeping onealiquot free of fiocculating agent as a control, and adding progressively increasing amounts of flocculating agent or mixture of fiocculants, and coupling agent when necessary, to the remainder; A particular ink is rolled onto a strip ofwhite enameled tin plate, leaving a sharp, white uninked margin. O'ne strip of wet-inked plate is dipped (white margin down) into'each varnishflocculating agent mixture, and thenallowed to drain. Bleeding, if present, will readily be observed against the background of the white enamel.

a roller.

acoaora preparation of finishing yarnis'hi-fioccula'ting agent aliquots, and rolling of a particular ink on a strip of white enameled metal plate is identical with the procedure described under bleeding. However, instead of dipping thestrip of wet-inked tin plate into the varnish, the varnish isapplied over the wetink by means .of The ,plate remains fiat at all times during this procedure. Ridging, if it occurs, can best be observed by looking at the ink from a 90 degree angle. v ,Ihave found that water is a very eif'ective flocculant in percentages of from about 2 to '10 per cent, but the practical range (which may be considered the critical range) is wider and extends from about 1.0 per cent to 12 per cent, depending upon the varying factors heretofore mentioned. Where a coupling agent or mutual solvent is 7 required, I found that the most satisfactory compounds are those which have a group that is water-like in character or which may be said to impart water soluble characteristics. The most desirable coupling agents all have a free organic hydroxyl or alcohol group or an acetylated alcohol group and all come under the classifications of aliphatic alcohols and glycol monoethers or acetates of the latter. They may be graphically represented by R(O)R' in which R is a straight chain aliphatic carbon chain of four (4) to eight (8) carbon atoms or a glycol monoether in which both the glycol and ether portions of the molecule have from two (2) to four (4) carbon atoms, and R is a hydrogen atom or an acetate radical.

The following are suitable as coupling agents either singly or in combination for all my purposes.

Butyl alcohol (butanol) Hexyl alcohol (hexanol) Octyl alcohol (octanol) Ethylene glycol monobutyl ether (Butyl Cellosolve) Ethylene glycol monoethyl ether (Cellosolve) Diethylene glycol monobutyl ether (Butyl Carbitol) Acetic ester of diethylene glycol monobutyl ether (butyl Carbitol acetate) The film forming materials from which metal decorating finishing varnishes are generally prepared and with which the principles of the present invention may be successfully employed include:

A. POLYESTER POLYMERS Alkyd resins Alkyd resins formed by the reaction of polyhydric alcohols and polybasic carboxylic acids and their anhydrides, modified with non-drying, semi-drying or drying oils, with or Without rosin, with or without mono or poly-functional phenolic bodies.

ether I Polymers of. dibastc. acid estcrso unsaturated monohydric alcohols 3. 29.6% Diallyl phthalate (solid) (film former) 29.6% Acetic ester of diethylene glycol monobutyl ether (resin solvents) 14.8% Diacetone alcohol p 3.8% Water (fiocculant) 22.2% Diethylene glycol monobutyl ether (coupling agent) Vinyl ester polymers 28.7% Toluene (resin solvent) 6.6%. Water (fiocculant) 31.7% Diethylene glycol monobutyl ether (coupling agent) }resin solvents 3 C. CONDENSATION POLYMERS OF'ALDE- HYDES AND AMINES OR ALCOHOLS 1. 80.0% Melamine aldehyde resin solution 50% solids (film former) v 3.2% Water (fiocculant) 16.8% Diethylene glycol monobutyl ether (coupling agent) 2. 82.0% Urea-melamine aldehyde resin 50% solids (film former) 3.3% Water (fiocculant) 14.7% Diethylene glycol monobutyl (coupling agent) Condensation polymer of a polyvinyl alcohol and aldehyde Polyvinyl butyral (solid) (film former) Butanol (resin solvent) Water (fiocculant) Ethylene glycol monobutyl ether (coupling agent) Polyvinyl butyral (solid) (film former) 43.2% Butanol (resin solvent) 3.9% Water (fiocculant) 46.2% Ethylene glycol monobutyl ether (coupling agent) D. COPOLYMER OF VINYL AND VINYL ESTER Vim/Z chloride-vinyl acetate polymer 1. 14.4% Vinyl chloride-vinyl acetate (solid) (film former) 25.2 Methyl isobutyl ketone 21.5% Xylene 10.8% Isophorone 2.9% Water (fiocculant) 7 25.2% Diethylene glycol inor'iobuti'rlv "ether, (couping agent) 1 solution ether resin solvents E. ROSIN MODIFIED OLEORESINOUS VARNISI-I 7 ether (coupling agent) The formulae cited are typical examples of my inventions. Many more could be added.

A lubricant may be added to the finishing varnish if the sheet metal is to be subjected to fabricating processes after lithographing. The addition of a lubricant (which is optional) Will, of course, vary the indicated percentages of ingredients to a slight degree. Customarily, the lubricant is added in the formbf a'solution and the amount is regulated so that the lubricant solids are equivalent to approximately 2 to 4 per cent of the resin solids in the finishing varnish.

The inclusion or exclusion of a'lubricating material has been found to be without effect on the pigment flocculating ability of the water.

The finishing varnish may be prepared without regard to whether the entire film former is manufactured in a single operation, or if a "hard resin is first formed and then combined with a drying oil in a varnish kettle orif a solid resin is dissolved in solvents. Further, these groups of film formers may be usedsingly, or in any compatible combination, depending on the film characteristics desired. Any one skilled in the art of varnish making will be able to prepare the various varnishes which may be used in connection with my disclosed invention.

The above examples are for the purpose of iilustrating the essential spirit of the present invention that is to say the finishing varnish is formulated in such a manner as to enable the same to induce a flocculated structure in the lithographic ink.

My extensive experiments conclusively indicate that the finishing varnishes covered by the invention hereinbefore described may be applied over any and all wet lithographic inks composed of organic and/r inorganic pigments dispersed in a drying oil and/or resin modified drying oil and/or other ink vehicles such as are ordinarily used in lithography, especially metal lithography.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes or modifications may be made in the compositions described without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the compositions hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. A finishing varnish for application over wet lithographic ink, said varnish consisting of an alkyd resin admixed with a drying oil as a film forming ingredient, a volatile organic solvent for said ingredient, i to 12 per cent based on the weight of the finished varnish of water as an ink pigment fiocculant, said volatile solvent being miscible with the ink vehicle and containing sufiicient coupling agent selected from the class consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

2. A finishing varnishfor application over wet lithographic ink, said finishing varnish consisting of an organic solvent soluble alkyd resin as a film forming ingredient, l to 12 percent by weight based on the finished varnish of water as an oil immiscible-water soluble polar liquid ink pigment fiocculating agent, a volatile organic solvent for said resin and said fiocculating agent, saidvolatile solvent being miscible with the ink vehicle and containing sufiicient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with a hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

3. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of an organic solvent soluble synthetic resin selected from the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, resinous polyethers of polyhydroxy compounds, resinous condensation polymers of amines and aldehydes, resinous condensation polymers of polyvinyl alcohol and aldehydes, and copolymers of vinyl halides and organic acid vinyl esters as film forming ingredients, 1 to 12 percent by weight based on the finished varnishof water as an oil immiscible-water solublepolar liquid ink pigment flocculating agent, and a volatile organic solvent for said resin and said flocculating agent, said volatile solvent being miscible with the ink vehicle and containing sufiicient glycol monoether having from 2 to 4 carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other etherified with a hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

4. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of an organic solvent soluble synthetic resin selected from the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, resinous condensation polymers of amines and aldehydes, resinous condensation polymers of aldehydes and polyvinyl alcohol and copolymers of vinyl halides and organic acidvinyl esters as film forming ingredients, 1 to .12 percent by weight based on the finished varnish of water as an oil immiscible-water soluble flocculating agent, and a volatile organic solvent for said resins and said fiocculating agent, said volatile solvent being miscible with the ink vehicle and containing sufficient unsubstituted monohydric alkanol having from 4 to 8 carbon atoms to maintain the ingredients in a single liquid phase.

5 A finishing varnish for application over Wet lithographic ink, said finishing varnish consisting of an organic solvent soluble synthetic resin selected from the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, resinous condensation polymers of amines and aldehydes, resinous condensation polymers .Of aldehydes and polyvinyl alcohol, andcopolymers of vinyl halides and organic acid vinyl esters as film forming ingredients, 1 to 12 percent by weight based on the finished varnish of water as an oil immiscible-water soluble polar liquid ink pigment flocculating agent, and a volatile organic solvent for said resins and said flocculating agent, said volatile solvent being miscible with the ink vehicle and containing sufficient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms to maintain the ingredients in solution in a single liquid phase.

6. A method of varnishing over wet lithographic ink comprising, printing a pigmented lithographic ink on a sheet of web material and fiocculating the ink pigment by applying over the wet ink a finishing varnish containing, an organic solvent soluble film forming resin in solution in a volatile organic solvent, 1 to 12 per cent by weight based on the finished varnish of water as an oil immiscible-water soluble pigment fiocculating agent, said volatile solvent being miscible with the ink vehicle and containing sufficient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

7. The method of claim 6 in which the resin is a synthetic resin.

8. The method of claim 7 in which the resin is a polymer of a compound containing a vinyl group.

9. The method of claim 8 in which the resin is a copolymer of a vinyl halide and an organic acid vinyl ester.

10. The method of claim 7 in which the resin is selected from the group consisting of alkyd resins, polymerized dibasic acid esters of unsaturated monohydric alcohols, organic acid polyvinyl esters, resinous polyethers of polyhydroxy compounds, resinous condensation polymers of amines and aldehydes, resinous condensation polymers of polyvinyl alcohol and aldehydes, and copolymers of vinyl halides and organic acid vinyl esters.

11. The method of claim 10 in which the resin is an alkyd resin.

12. The method of claim 10 in which the resin is a condensation polymer of an amine and an aldehyde.

13. The method of claim 10 in which the resin is a resinous ether of a polyhydroxy compound.

14. The method of claim 10 in which the resin is a condensate of a polyvinyl alcohol and an aldehyde.

15. The method of claim 6 in which the web material is a metal sheet.

16. The method of claim in which the metal sheet is tin plate.

17. The method of claim 15 in which the metal sheet is steel.

18. The method of claim 10 in which the coupling agent is an unsubstituted monohydric alkanol having from 4 to 8 carbon atoms.

19. The method of claim 10 in which the coupling agent is a glycol monoether having from 2 to 4 carbon atoms in the glycol portion" of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with an allphatic hydrocarbon substituent having from 2 to 4 carbon atoms.

20. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of an organic solvent soluble polyvinyl ester of an organic acid as a film forming ingredient, 1 to 12 per cent by weight based on the finished varnish of water as an ink pigment flocculant, and a volatile organic solvent for said ingredient, said volatile solvent being miscible with the ink vehicle and containing sufiicient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethersin which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

21. A finishing varnish for application overwet lithographic ink, said finishing varnish consistv as a film forming ingredient, l to 12 per cent by weight based on the finished varnish of water as an ink pigment flocculant, and a volatile organic solvent for said ingredient, said volatile solvent being miscible with the ink vehicle and containing sufficient coupling agent selected from the class consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

22. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of a resinous copolymer of a vinyl halide and an organic acid vinyl ester as a film forming ingredient, l to 12 per cent by weight based on the finished varnish of water as an ink pigment fiocculant, and a volatile organic solvent for said copolymer, said volatile solvent being miscible with the ink vehicle and containing sufiicient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon chain having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

. PAUL W. GREUBEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,898,709 Belfit Feb. 21, 1933 2,044,572 Hollabaugh June 16, 1936 2,392,135 Farr Jan. 1, 1946 2,436,954 Denton Mar. 2, 1948