US2354979A - Antioffset composition - Google Patents

Description

, faces.

of the desired lands.

Patented Au -1, 1944 2,354,979 ANTIOFFSET coMrosrrIoN Ernest G. Alm'y, Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application April 15,1942,

Serial No. 439,107

Claims.

the sheet next to it. A number of methods have been devised to eliminate or minimize offset. One procedure has beento protect the ink film by spraying the sheets after printing with an anti-offsetting medium which deposits -lands or projections higher .than the ink film on the printed sheet to protect it from adjacent sur- Such a method .is that described in U. S. Patent No. 2,078,790, issued April 27, 1937, to Edmond H. Bucy. This patent teaches employing an anti-ofiset medium which comprises a land-forming ingredient contained in an evaporable solvent. The anti-offset, composition is sprayed onto the sheets in such manner that the solvent volatilizes as the droplets travel to the sheet, producing small, dried or partially dried,

particles which adhere to the sheet in the form Another anti-onset method Bucy Patent No. 2,142,666, issued January 3, 1939. According to this method, the inked surface is contacted with a roller, the surface of which contains numerous, small depressions or pits holding anti-ofiset composition. Composition deposits from the roller onto the inkedsurface to form the lands. Thepits in the roller are then refilled with anti-offset composition for further application. This method particularly adapted for preventing offset on work from web-fed presses.

- A number of compositions have been devised which are useful in the Bucy processes. "Two, which are the subject matter of Bucy Patents Nos. 2,111 2,667 and 2,142,668, issued January 3, 1939, employ land-forming materials such as cellulose esters .or ethers and two solvents, one more readily volatile than the other.

It is an object of the present invention to provide for the prevention of offset by the application of new anti-offset processes and compositions.

It s further among the objects of the invention 0 provide anti-offset compositions which are economical to use and readily-applied.

Often, and especially in multicolor work, each sheet is separately printed a number of times. Some prior art anti-offset compositions, while adequately effective for preventing ofiset, have shown a tendency to be picked up from the treated surface when a second impression is made.

is described in The picked-up composition deposits in with the rest of the raised surfaces. An undesirable blurred print results. Some ofiset compositions on drying have also caused abrasion to printing equipment, limiting. the life of rolls in presses through which printed matter may subsequently pass. Another object of the present invention is the production of anti-offset compositions which will have improved characteristics of pick-up and abrasion on presses.

Other objects will be apparent from the following descriptiorn It has been found that solutions of combinations of a soluble organic compoundcontaining at least 3- hydroxyl groups, a boric-acid producing material, and alkali are excellent anti-oifset compositions.

The soluble organic compounds containing at least 3 hydroxyl groups usable for'this invention preferably are ones containing a chain ofno more than 6 carbon atoms. are the polyhydric compounds, glycerol, erythritol, pentitols, pentoses, hexitols and hexoses.

As alkalies can be used any of the alkalies containing an alkali metal, ammonia, or watersoluble amines, such as triethanolamine. By alka1ies as used irrthis specification are meant those containing akali metal, ammonium or water-soluble amine radicals.

As a boric-acid producing material can be used any boron compound which forms orthoborlc acid, HsBOa in solution, such as metaboric acid, HBOz, tetraboric acid, HzB-iOv, or boron trio zide, B203. Both alkali and boric-acid producing material may be, at least in part, simultaneously provided by borate salts of the alkalies,- as, for

example, borax.

An anti-offset composition of the, present invention may be readily prepared by dissolving the separate ingredients in water. Whether or not a reaction occurs amongst the ingredients so-dissolved is at present not known. If hydroxy-containing organic compounds of the typeherein employed and boric 'acid are heated together so as to drive off water, organic borate resins are formed which contain-a borm acid molecule condensed with the hydroxyl-containing organic compound molecule: For example,.

sorbitol monoborate dicondensation product may be formed from the reaction of 1 mol of boric acid and 1 mol of sorbitol. Each boron atom in the resin contains a residual acid hydroxyl group which may be reacted with alkali with the resultant formation of alkali sorbitol borate. The reactions of boric acid with the other hydroxylcontaining organic compounds of the type used Examples of such and the alkali are dissolved separately in water or whether combined forms of these ingredients are dissolved in water. For example, employing sorbitol as exemplary of the hydroxyl-containing organic compound, the combination of this invention may be prepared by dissolving sorbitol,- alkali and'boric acid in water separately; it may also be prepared by dissolving alkali sorbitol borate in water; it may be 'further'prepared by dissolving sorbitol borate and alkali in water: or again it may be prepared by dissolving sorbitol and an alkali borate, such as borax, in water.

It is usually preferred to employ the organic compound containing at least 3 hydroxyl groups and the boric acid material in proportions such that they will be approximatelyone atom of boron for each molecule of organic compound. These proportions are not' highly critical, but sometimes, if too little boric acid material is employed, the excess organic compound will plasticize the lands, making them too soft. On the other hand, too much boric acid material may result in a crystallizing out of boric acid from the solution before it is applied.

The properties of these new anti-offset compositions difier somewhat depending upon the particular organic compounds employed. Hardness of the lands and their efllciencyas an antiofiset medium appears to increase, in general, with the number of hydroxy groups and chained carbon atom-s in the organic material used. Glycol compositions are too soft for much commercial use. Glycerine compositions are harder and can be used if sufficiently concentrated. Hexitols, particularly sorbitol compositions, apparently produce the most workable solutions. Hexose compositions, for example, glucose, have the advantage of very low cost, but solutions prepared with hexoses are not as stable to standing as are the hexitols. Because of their cheapness, however, they have many anti-offset applications.

Control of the amount of alkali present in the composition efiects to a considerable degree regulation of the Properties of the lands. After hydroxyl-containing organic compounds have been reacted with boric acid to produce borate resins, each atom 'of boronhas still attached to it an acid hydrogen "atom which may be reacted with one equivalent of alkali. The resin exhibits properties of increased viscosity and hardness as the alkali content increases toward complete satisfaction of all molecules containing an acid group. Similar properties of increased hardness may be noticed in the lands produced from anti-offset solutions of this invention when they are prepared with increased concentrations of alkali. This effect is apparently-related'to the property of the alkali of making the drops crust over on evaporation. This is desirable because the droplets appear to be dry on their surfaces and less permanently to the paper so that a permanently rough surface need not be produced. The

.ability to change the character and particularly the hardness of the lands by variation in the alkali content or pH of the anti-offset solution is an important advantage of this invention, for it provides an easy method of suiting the lands to the particular job in-hand. Preferably, the

2,354,979 compound, the boric acid producing material,

mately 0.5 to 1 gram equivalent of alkali per gram atom of boron present. A solution containing 0.5 equivalent of sodium per atomic weight of boron is conveniently made by adding borax (Na2B4O'1 in which the ratio of sodium to boron is 0.5) to a solution of hydroxyl-containing organic compound of the type employed in this invention. For example, if 1 mol of sorbitol and 0.25 mol of borax are added to water, a solution is obtained equivalent to that where a 0.5 alkali reacted sorbitol borate is dissolved in water. It is usually preferable not to employ more than one equivalent of alkali per gram atom of boron because the lands become over-brittle and excess alkali may harm some papers. Below a 0.5 equivalent of alkali per atomic weight of boron, the skin-forming effect is largely lost. For some work a solution corresponding to a sorbitol borate reacted with 0.95 equivalents of alkali per. mol of borate has been found ideal. As indicated above, however, the alkali content should be adjusted for the particular job to be performed.

The proportion of solids in the solution is not at all critical but will depend largely on the type of printing for which the solution is prepared. Also it depends greatly on the particular organic compound employed. Glycerine requires more concentrated solutions than do the hexitols. Thus work using heavy inks on coarse papers generally requires larger lands than does finer work. Usually, more concentrated solutions are more viscous and will give larger lands than those of less concentration. Forv spraying purposes it has been found that less concentrated solutions are generally required than for the roll process.

A low boiling solvent more volatile than water such as, for example, dioxane, acetone, or watermiscible alcohols such as methyl, ethyl, or isopropyl alcohol, is conveniently added to antioffset compositions of this invention as a drying aid.

It has been found that the spraying properties of these anti-offset solutions may be improved very appreciably by the addition of small proportions of an agent which is compatible with the solution and which exhibits gelatinizing tendencies therewith. Some gums have been found suitable for this purpose. Gum karaya, gum arabic, and locust gum are preferred examples of these. Other materials which may be employed are polyvinyl alcohol and starch acetate in their water-dispersible modifications. The improvement effected by these gelatinizing agents is a lessening of the proportion of total solids necessary to provide a usable composition. When one of them is present, a less concentrated solution is substantially equivalent to a more concentrated, and, hence,-more expensive solution prepared without a gelatinizing agent. The reasons for this are not fully understood, but, without any intention to limit the invention to the correctness of the explanation, it is suggested that the action of the gelatinizing substance is two fold. The viscosity of the solution is increased moderately, and the solution becomes stringy, exhibiting an increased property of cohesiveness. Both of these efiects, and particularly the latter, make for coarser atomization from the spray gun, so that the average particle size of the spray is larger and less of the solution is wasted in forming fines which do not produce the desired lands.

solutions of this invention contain from approxi- The anti-offset composition of the invention may also contain inert ingredients contained in other anti-offset ciunpositions providing they are operative therewith. A few examples of ingredients to improve them.

viously prepared solution of gum karaya in the such ingredients are: organic soaps. such as aluminum stearate. aluminum palmitate, r zinc stearate, or materialssuch as asbestine, diatomaceous earth, fullers earth, magnesium carbonate, talc, powdered mica, powdered magnesium, powdered aluminum hydrate, a starch such as corn starch, etc. Furthermore, the compo.-

sitions of this invention may be added to other anti-ofiset compositions containing such or other The solutions of thisinvention may applied in any convenient manner. Spray and roller techniques are known in the art. It is Example 1- An anti-oil'set solution was prepared with the following ingredients:

Percent by weight Sodium sorbitol borate 33.3 95% ethyl alcohol 11.1 Water 55.6

The borate was prepared by heating equimolar 1 parts of a non-crystallizing sorbitol of the type disclosed in U. S. Patent No. 2,172,357, issued September 12, 1939, to K. R. Brown, though cryscomposition. This solution when applied in the usual manner was found to be excellent in producing lands which eliminated oflset without perceptible roughening of the, surface, and also did not show the pick-up and abrasive properties characteristics of some prior art solutions. The solution. also showed no tendency to clog 'up spraying equipment.

Example 2 This example shows how the addition of a small quantity of a gum such as gum karaya will permit the use of lesser solids concentration.

A solution of the following composition exhibited much the same spraying properties as did the solution of Example 1.

Percent by weight Sodium sorbitol borate 20 95% ethyl alcohol 10 Gum karaya 0.1 Water 72.9

'in Example 1. It was diluted with one-third its weight of water and finally stirred into a prealcohol and the remainder of the water.

Example 3 This example shows the preparation of a specific anti-offset solution by mixing boric acid, alkali, sorbitol, gum karaya and alcohol. An open mixing tank was provided with heating and cooling coils for assisting the dissolving of the ingredients, a thermometer and agitating means. In this tank 530 lbs. of water containing 30 grams of sodium hydroxide were heated to 50 C. With vigorous agitation a slurry of 510 grams of gum karaya in one liter of alcohol was added slowly. Agitation was continued for two hours, the temperature being maintained between about 45 and 50 C. The following ingredients were then added in succession and without artificial heating:

- Pounds Caustic soda solution (49.6% NaOH) 30 Boric acid h 40 Caustic soda solution (49.6% NaOI-I) 20 Sorbitol syrup (84.6% solids) -13? was stirred for 9 hours and then made an excellent anti-onset composition.

It'should again be pointed out that the concentrations at which these solutions are employed are not critical. The solution shown in Example 1 has been used for spray purposes with solids contents of from 25 to 50%. At the-upper ranges of concentration the spray becomes syrupy and uneeonomical to use. At lower ranges when spraying the spray guns must be opened-too wide and the amount of spray floating in the air becomes objectionable in the press room. Hence the middle concentrations are somewhat more satisfactory, though spray gun openings and other operational technique will compensate tor wide ranges 02- concentration.

What is claimed is:

1. An anti-offset composition which comprises an aqueous solution oi a combinatlon'oi a soluble organic compound selected fromthe group consisting of glycerol, erythritol, pentitols, pen- 'claim 1 in which the organic compound is a hexose.

5. An anti-ofl'set composition according to claim 1 in which the organic compound is a hexitol and the alkali is present in proportions of about to 1 equivalent of alkali to each atomic weight of boron.

6. An anti-onset composition according to claim 1 which also contains a further solvent which increases the volatility oi the solution.

fl. An anti-oflset composition according to claim 1 which also contains a gelatinizing agent. a. A composition according to claim 1 in which the organic compound is a hexitol, and the solution also contains a further solvent which increases its volatility and a gelatinizing agent.

9. A composition according to claim 1 in which the organic compound is glycerol, and the solution also contains a further solvent'which 'increases its volatility and a gelatinizing agent.

10. A composition according to claim 1 in which the organic compound is a hexose, and the solution also contains a further solvent which increases its volatility and a gelatinizing agent.

11. An anti-offset composition which comprises an aqueous solution of a combination of a hexitol, a boric acid producing material, a sma proportion of locust bean gum, and a water-miscible alcohol, said composition forming resinous material on drying.

5 13. A process of preventing oifset from inked surfaces which comprises spraying onto the inked suriacea composition which comprises an aqu'e ous solution of a combination of a hexitol, a boric acid producing material, and an alkali, the spray 1o distance, size, and quantity being so adjusted thatanti-offsetting lands are produced upon the inked surface. l

4 14. A process according to claim 13 in which the inked surface is heated prior to spraying.

15 15. A process according to claim 13 in which the combination also contains a. water-miscible alcohol and gum karaya,

. ERNEST G. ALMY CERTIFICATE CORRECTION. Patent No. 25551;,979. August 1, 191411..

ERNEST G. ALHY. 1

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: I Page 1, first column, line 60,- for "ad" reed--and--; page 2, first column, line 6h, for "most" read --more--; and that the said Letters Patent should be read with 'this correction therein that the same may confom to the'record of the case in the Patent Office, I

Signed and sealed this 5th day of September, A. D. 191m.

Leslie Frazer Acting Commissioner of Patents.