IMPROVED LITHOGRAPHIC INK COMPOSITION

Abstract: A lithographic ink has an oil-soluble buffer incorporated thereinto, the additive producing beneficial effects with respect to reducing the pH drift of the ink during use. The buffer is produced by combining a primary, secondary, tertiary, or quaternary amine with an at lest dibasic organic acid.

Description: In the art of lithographic printing, an oleophilic, oil-based printing ink composition is mixed with a water-based, oleophobic fountain solution. Immediately after the mixing of the oil ink with the fountain solution, a water-in-oil emulsion is created by subjecting the combination of ink and fountain solution to severe turbulence and shear. Shortly after the water-in-oil emulsion is made, the emulsion contacts a printing plate which has both oleophilic and oleophobic surfaces thereon. If the pH of the fountain solution is not within the proper range, image definition at the interface between oleophilic and oleophobic regions is blurred, reducing image resolution and occasionally causing smudging. In the process of the prior art, a water-soluble buffer is incorporated into a fountain solution (e.g. WO 84/021 42). During the printing process, the buffered fountain solution is combined with and emulsified within an oleophilic ink. A water-in-oil emulsion is formed thereby. The buffer, preferring the aqueous fountain solution, remains within the fountain solution. Since there is no significant oil-solubility for any significant exchange of buffer from the hydrophilic fountain solution to the oleophilic ink, the result is that virtually all of the buffer remains within the fountain solution. Thus, at the interface between the fountain solution and the ink, the availability of buffer at the interface region is "one-sided." In other words, the only buffer reaching the interface to control pH drift is buffer supplied from the fountain solution side of the interface. The object of the invention was to provide lithographic ink compositions which avoid the disadvantage of art ink compositions, viz., a rise in the pH value during the printing process. The present invention pertains to an improved lithographic ink composition comprising at least 0.1 percent, based on weight of ink composition, of a substantially oil-soluble buffer. The present invention utilizes an oil-soluble buffer. The buffer is added to the oleophilic ink. The ink and fountain solution are then combined and a water-in-oil emulsion is formed, with the resulting emulsion being used immediately thereafter in the printing process. The vast majority of buffer remains in the oleophilic ink phase. A minor proportion of the acid portion of the buffer (i.e. that which is disassociated) migrates into the fountain solution. In comparison with the prior art, there is a greater balance between the amount of buffer in the ink and the amount of buffer in the fountain solution. The result of this balance is a greater availability of buffer to the interface. This greater availability of buffer to the interface provides greater pH control (i.e. less pH drift) during the resulting printing process. The buffer is an oil-soluble salt, which acts as a buffer to stabilize the pH of the ink and fountain solution with which the ink is combined. The oil-soluble buffer is the product obtained by reacting a primary, secondary, tertiary, or quaternary amine with an organic acid with at least two carboxylic acid groups. The oil-soluble amine is combined with the acid in a molar ratio of between 1:1 and 2:1. Preferably the molar ratio of the amine-to-acid is approximately 1:1. Suitable amines are aliphatic oil-soluble monoamines which are primary, secondary, tertiary, or quaternary amines of which the carbon chain may be saturated or unsaturated, branched or straight. Examples of such amines are octylamine, N,N-diethyl propylamine, decylamine, n-dodecylamine, tetradecyl amine, n-octadecyl amine, cocoamine, dicocoamine, dimethylcocoamine, methyl dicocoamine, cocotrimethyl ammonium chloride, dicocodimethyl ammonium chloride, tallow amine, dimethyl tallow amine, tallow trimethyl amine, hydrogenated tallow amine, dihydrogenated tallow amine, dimethylhydrogenated tallow amine, methyl dihydrogenated tallow amine, dihydrogenated tallow dimethyl ammonium chloride, oleylamine, dimethyl oleylamine, soyaamine, dimethyl soyaamine, disoyaamine, soyatrimethyl ammonium chloride, stearyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride and cetyl trimethyl ammonium chloride. Preferred amines are believed to be cocotrimethyl ammonium chloride, dicocodimethyl ammonium chloride, dihydrogenated tallow dimethyl ammonium chloride, stearyl trimethyl ammonium chloride, lauryl trimethylammonium chloride and cetyl trimethyl ammonium chloride. The most preferred amine is dihydrogenated tallow dimethyl ammonium chloride. The organic acid has at least 2 carboxyl groups thereon. Suitable acids are dibasic water-soluble organic acids such as oxalic, malonic, succinic, glutaric, adipic, pimelic, maleic, malic, tartaric, and citric. Preferred acids are adipic acid and citric acid. The most preferred polybasic acid is citric acid. The substantially oil-soluble buffer used in the present invention has a solubility of at least 1 gram per liter in the oleophilic ink. However, preferred are buffers which have a solubility of at least 20 grams per liter in the oleophilic ink. Preferably stabilized lithographic inks are those containing C.I. Pigment Red 57:1; C.I. No. 15 850:1. The oil-soluble buffers may be added to the finished lithographic inks, or added during the manufacture of the inks from the pigment. Example 1 a) Preparation of the buffer. 57 grams of 75 percent active dimethyl(hydrogenated-tallow)ammonium chloride were dissolved in 100 grams methanol, and 18 grams of citric acid were dissolved in 50 grams of methanol, after which the two solutions were mixed together, at room temperature. The methanol was then removed by evaporation, leaving the pure salt of the 75 percent active dimethyl(hydrogenated-tallow)ammonium chloride and citric acid. b) The salt from a) was then utilized as an additive to flush of pigment red 57:1. The pigment flush, herein designated Flush I, was made as described below. To determine what effect the additive had on both pH stability and bleed, the following process was carried out: (A) 50 grams of Flush I were weighed out on Mylar®, and placed on a hot plate at 230°F; (B) then 0.5 grams of the additive a) were weighed out and placed on top of Flush I; (C) Flush I and the additive were then thoroughly mixed together while on the hot plate; the mixing was carried out over a period of about two minutes; and (D) the mixture of Flush I and additive were then transferred to a glass slab and thoroughly mixed thereon. c) The additive/Flush I combination thus obtained was then tested for pH drift by carrying out the following procedure: 1. 50 grams of the test ink were placed in a Duke mixer; 2. the mixer was run for 50 revolutions; 3. 50 grams of the fountain solution were then added; 4. the mixer was run for 450 revolutions; 5. as much of the fountain solution as possible was decanted; and 6. the change in the pH of the fountain solution was calculated by measuring the pH of the fountain solution both before and after the fountain solution was mixed with the ink. Example 2 The additive was that of Example 1a). The additive was then used to prepare Flush II (see preparation details below). About 0.5 grams of the additive were combined with 50 grams of Flush II. The additive and Flush II were then mixed as described in Example 1b).The combination of additive and Flush II was then tested for pH drift (as described in Example 1c),with the results of these tests also being shown in Table I. Example 3 a) Preparation of the buffer: 20 parts octadecylamine were added to 51.1 parts of Magiesol 47. This mixture was heated to 200°F to obtain a clear solution. 10 Parts of adipic acid were then added to the clear solution. The adipic acid immediately reacted with the octadecylamine to form the soluble salt. b) The additive was then mixed with Flush I in the ratio of 1 gram additive to 50 grams of Flush I. The flush and additive were combined exactly as described in Example 1, and the test for pH drift was performed exactly as for Example 1c). The result of this test is also shown in Table I. Example 4 (Comparative Example) Flush I, having no additives therein, was subjected to a pH drift test as described in Example 1c). The result of this test is also reported in Table I. Example pH Drift Additive Level 1 0.05 1% 2 0.11 1% 3 0.67 2% 4 3.23 0% The advantageous effect of the additive on the flush is revealed by Table I. Each of Examples 1-3 evidenced significantly less pH drift than the control, Example 4. Preparation of Flush I A presscake contained 500 parts (21-22 percent) solids by weight of presscake) of C.I. Pigment Red 57:1; C.I. No. 15 850:1 pigment. The presscake was divided into six fractions of equal weight. Two of these fractions were added to a sigma blade mixer known as a flusher. The flusher was started. Steam was applied to the jacket until the temperature reached 65°C. Then the following materials were added: (a) 108 parts of a linseed oil alkyd; and (b) 179 parts of a mixture of 60 weight percent of a maleic acid modified rosin ester of abietic acid/40 weight percent Magiesol 47; after which the first break occured and the flusher was stopped. The clear aqueous phase was poured off. Four remaining breaks were then carried out as follows. One fraction (i.e. one sixth) of the presscake was first added to the flusher. The flusher was started again and heated to 65°C. A fraction of 149 remaining parts of 60 weight percent of a 140°C melting hydrocarbon resin/40 weight percent Magiesol 47 were added as needed to achieve each remaining break. The flusher was stopped after each break. With each break, the clear aqueous phase was decanted. After the last break was poured, the flusher was started, sealed and vacuum was applied. The flusher was run until the batch temperature reached 110°C. At this point the cold water was turned on the jacket, 60 parts of 60 weight percent of a maleic acid modified rosin ester of abietic acid/40 percent Magiesol 47 and 15 parts of water were added, and the flusher was stopped while still under vacuum. The flusher was occasionally started and quickly stopped over a period of fifteen minutes to allow for rapid cooling. After this point, the temperature of the batch was 70°C and the cold water on the jacket was turned off. The flusher was started, maintaining vacuum and the remaining flush thinning material composed of 320 parts of 60 weight percent of a maleic acid modified rosin ester of abietic acid/40 percent Magiesol 47 plus an additional 211 parts of Magiesol 47 were added as fast as possible. The vacuum was then shut off and the finished product removed from the flusher. Preparation of Flush II A presscake contained 500 parts (21-22 percent solids by weight of presscake) of C.I. Pigment Red 57:1; C.I. No. 15 850:1. The presscake was divided into four fractions of equal weight. Two of these fractions were added to a sigma blade mixer known as a flusher. The flusher was started. Steam was applied to the jacket until the temperature reached 65°C. Then 176 parts of 72 weight percent of a maleic acid modified rosin ester of abietic acid/28 weight percent Magiesol 47, along with 52 parts of a linseed oil alkyd were added to the flusher, after which a first break occured and the flusher was stopped. The clear aqueous phase was poured off. 125 additional parts of pigment in the form of one additional fraction of the presscake were added to the flusher. The flusher was started and again heated to 65°C. 150 parts of 60 weight percent of a 140°C melt hydrocarbon resin/40 weight percent Magiesol 47 were added, the second break occured and the flusher was stopped. Again, the clear aqueous phase was decanted. 125 remaining parts of pigment, in the form of the last remaining fraction of the presscake, were added to the flusher. The flusher was started and again heated to 65°C. 52 remaining parts of 60 weight percent of the 140°C melt hydrocarbon resin/40 weight percent Magiesol 47 were added, the third and final break occured, and the flusher was stopped. Again the clear aqueous chase was decanted. After the least break was poured, 77 parts of 72 weight percent of a maleic acid modified rosin ester of abietic acid/28 weight percent Magiesol 47 were added to the flusher. Then the flusher was started, sealed and vacuum applied. The flusher was run until the batch temperature reached 110°C. At this point, the cold water was turned on the jacket and 60 parts of 60 weight percent of a 140°C melt hydrocarbon resin/40 weight percent Magiesol 47 were added, along with 15 parts of water, and the flusher was stopped while still under vacuum. The flusher was occasionally started and stopped over a period of 15 minutes to allow for rapid cooling. After this point, the temperature of the batch was 70°C and the cold water on the jacket was turned off. The flusher was started, maintained vacuum and the remaining flush thinning material composed of: 361 parts of 60 weight percent of a 140°C melt hydrocarbon resin/40 weight percent Magiesol 47; and 65 parts Magiesol 47 was added as fast as possible. The vacuum was then shut off and the finished product removed from the flusher.

Claims: An improved lithographic ink composition comprising at least 0.1 percent based on weight of ink composition,of a substantially oil-soluble buffer. An improved ink composition as described in claim 1 wherein the buffer is a reaction product of a primary, secondary, or tertiary amine and an organic acid with at least two carboxylic acid groups. An improved ink composition as described in claim 1 or 2, wherein the buffer is a reaction product of a quaternary amine and an organic acid with at least two carboxylic acid groups. An improved ink composition as described in claim 2 or 3, wherein the organic acid is citric acid. An improved ink composition as described in claim 1, 2, 3 or 4, wherein the ink comprises C.I. Pigment Red 57:1; C.I. No. 15 850:1.

Inventors: FOYE, THOMAS EDWARD, MALCHICK, SHERWIN PAUL, PEPOY, LOUIS JOHN
Applicants: BASF CORPORATION
Application year: 1988
Main classification: C09D11
IPC codes: C09D11