Acrylic resins as binders for gravure inks

Field of the invention

0001This invention relates to acrylic resins. In particular, this invention relates to the use of acrylic resins as binders for solvent-based gravure printing ink formulations.

BACKGROUND OF THE INVENTION

0002One of the traditional problems facing gravure ink formulations has been low solution viscosities. These low viscosities make it difficult to formulate inks having the desired pigment-to-binder ratios at press viscosity that are necessary for this type of printing.

0003The high acid values common in rosins may be lowered by reacting them with zinc oxide, calcium acetate, or similar compounds to produce metallic resinates. Metal resinates are widely used as binders in gravure printing due to their rapid solvent release and their ability to prevent some basic pigments from livering. These resinates are soluble in hydrocarbons, but not in alcohol.

0004However, one of the shortcomings of using metal resinates in gravure inks has 0been their low solution viscosities (a by-product of their low molecular weights). These low viscosities lead to the same printing ink formulation problems referenced above.

0005A critical property of ink formulations that is directly linked to viscosity is dilutability. Viscosity is measured by the time required for an exact quantity of solution to flow by gravity through a specially sized apparatus. Dilutability is measured by the amount of solvent needed to reduce the viscosity of a given weight of resinate solution to a certain level. The typical specification calls for the volume of toluene needed to reduce 100 grams of resinate to 18 seconds as measured with a #2 Shell cup. While common dilutability values of commercial resinates are between 70 to 120 ml, ink makers would like dilutabilities higher than this in order to be able to achieve a desirable balance of solids, colour strength, and viscosity in finished inks.

0006To solve these problems of viscosity and dilutability, ink makers traditionally have added small amounts of ethylcellulose (E/C) or ethylhydroxyethylcellulose (EHEC) to the ink as a dilution enhancer (the properties of which are discussed in U. S. Patent No. 2,610,180). EHEC owes its thickening ability to three factors: (a) a very high molecular weight, (b) a rigid molecular structure, and (c ) intermolecular association via hydrogen bonding of unetherified hydroxyl groups on the cellulose backbone. In this way E/C or EHEC can be used to produce a drastic reduction in resin solids at press viscosity (expressed in the industry as a "high dilution").

0007However, the use of E/C or EHEC may give rise to other problems, as described in Leach, R. H., <u>The Printing Ink Manual,</u> Van Nostrand Reinhold Co. Ltd., London, 1988. Very small amounts of these compounds can cause substantial reductions in the gloss of an ink. Moreover, these compounds are relatively expensive. Finally, E/C and EHEC have demonstrated resinate incompatibilities which seem to vary from batch to batch, and may manifest itself in phase separation of the ink upon standing.

0008Attempts have been made to avoid these problems by producing other binders which can be used as dilution enhancers. For example, U. S. Patent No. 3,468,829 teaches the preparation of printing ink binders based on reaction products of: 1) natural resins, 2) other synthetic resins (for example, hydrocarbon resins having a bromine number of 5 to 80), and 3) calcium compounds (and, if appropriate, other compounds of group II of the periodic system). The patent also teaches reacting an unsaturated dicarboxylic acid (i. e. maleic anhydride) at the same time. However, this process has a disadvantage in that the resulting viscous products are virtually not utilizable as printing ink binders.

0009Other known binders are taught in U. S. Patent Nos. 4,528,036 and 4,552,592. Here, the binders are based on the reaction products of: 1) natural resins, 2) a copolymer or a synthetic resin, and 3) calcium compounds. The resulting reaction products are reacted subsequently with acetic acid to form a salt of the corresponding resin. However, these solutions are of relatively low molecular weights and viscosities.

0010Yet another known binder is the product complex formed by reaction of a metal resinate and an amine-reactive polyamide as taught in U. S. Patent No. 4,767,835. The amine-reactive polyamide, being a condensation polymer, is of comparatively low molecular weight.

0011U. S. Patent No. 4,289,678 teaches an acrylic thickener for use in formulating gravure inks. This thickener, the reaction product of an addition polymerisation reaction, has a molecular weight in the range of 100,000 to 2,000,000. This large molecular weight may cause incompatibility problems for ink formulators similar to those exhibited with E/C and EHEC.

0012Commonly assigned U. S. Patent No. 5,098,479 teaches dilution enhancing aminoacrylate resin binders. However, as amine-containing monomers are employed in the production of these binders, they are primarily suitable for use in formulating zinc-containing metal resinate inks (i. e., they give little or no dilution enhancement in zinc-free resinates).

0013Despite the development of these, and other, thickeners E/C and EHEC remain the preferred viscosity extenders in the field. Therefore, it is an object of this invention to produce economical, dilution enhancing binders for use in formulating gravure printing inks.

0014Another object of this invention is to produce hydrocarbon-soluble binders which, when used to formulate gravure printing inks, enhance both the gloss and the colour properties of the inks.

0015A further object of this invention is to produce gravure printing ink formulations with enhanced gloss and colour characteristics.

SUMMARY OF THE INVENTION

0016These objects are achieved by the production and use of hydrocarbon-soluble resins which are suitable for employment as binders in formulating notably inks, in particular gravure printing inks. These binders are the solution polymerisation reaction product of: 1) an alkyl or cycloalkyl ester of acrylic or methacrylic acid, 2) styrene or alkylated styrene, 3) a carboxyl-containing monomer, and where desired, 4) a difunctional ethylenically unsaturated monomer.

0017Studies have shown that gravure printing inks formulated with these relatively inexpensive binders exhibit dilution properties which are economically comparable to those displayed by inks formulated with E/C or EHEC (see Examples below). Moreover, inks formulated with these binders have superior gloss and colour characteristics when compared to inks formulated with E/C or EHEC.

0018Other invention embodiments are set forth in the claims which are incorporated in the specification in their entirety by reference, including the use of said binders notably for the manufacture of inks , and in particular for gravure printing inks.

DESCRIPTION OF THE PREFERRED EMBODIMENT

0019The invention is the production and use of hydrocarbon-soluble resins as binders notably for the manufacture of inks, in particular for gravure printing inks. These binders are the solution polymerisation reaction products of: <ul id="ul0001" list-style="none" compact="compact"><li>(a) about 50.0% to about 99.0% by weight of a member selected from the group consisting of styrene, alkylated styrene, and combinations thereof;</li><li>(b) up to about 50.0% by weight of a member selected from the group consisting of alkyl esters of acrylic acid, alkyl esters of methacrylic acid, cycloalkyl esters of acrylic acid, cycloalkyl esters of methacrylic acid, and combinations thereof;</li><li>(c ) about 0.2% to about 20.0% by weight of a carboxyl-containing monomer; and</li><li>(d) up to about 2.0% of a difunctional ethylenically unsaturated monomer.</li></ul>

0020From about 50% to about 99% by weight of the reactants suitable for use in the solution polymerisation reaction which produces the binder composition must be a member selected from the group consisting of styrene, alkylated styrene, and combinations thereof. The preferred range for these reactants is from about 80% to about 95%.

0021Up to 50% y weight of the reactants may be an alkyl or cycloalkyl ester of acrylic or methacrylic acid. The preferred range for these esters is from about 5% to about 20%. Suitable alkyl or cycloalkyl esters of acrylic or methacrylic acids include, but are not limited to, the following: butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, ethyl acrylate, isobornyl methacrylate, isodecyl methacrylate, and combinations thereof.

0022From about 0.2% to about 20.0% by weight of the reactants may be a carboxyl-containing monomer or combination of monomers. The preferred range for these monomers is from about 1.0% to about 10.0%. Suitable carboxyl-containing monomers include, but are not limited to, the following: acrylic acid, methacrylic acid, itaconic acid, and combinations thereof.

0023Suitable difunctional ethylenically unsaturated monomers include, but are not limited to, the following: divinylbenzene, diethylene glycol diacrylate, tripropylene glycol diacrylate, allyl methacrylate, and combinations thereof.

0024While the solution polymerisation reaction may be thermally driven, it is preferred to utilise a free-radical polymerisation initiator. The type of free-radical polymerisation initiator suitable for use in the reaction is known in the art to depend upon the desired temperature for the reaction. Typical initiators include, but are not limited to, the following: di-tert-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, t-butyl peroctoate, azobisisobutyronitrile, benzoyl peroxide, and combinations thereof.

0025The present binders are the polymer reaction products of solution polymerisation reactions. Suitable binders will have a number average molecular weight in the range from about 4,000 to about 80,000.

0026Solvents suitable for use in the reaction and in formulating the gravure inks include both aliphatic and aromatic hydrocarbons.

0027Where desired, the gravure printing ink formulation may include a resinate in addition to a pigment and the present binder composition. Suitable resinates for use in conjunction with the present binder may be prepared by metallisation (i. e. the production of metal salts) of a member selected from the group of rosins including rosin, phenolated rosin, polymerised rosin, maleated rosin, fumarised rosin, and combinations thereof, with a member selected from the group consisting of zinc, calcium, magnesium, and combinations thereof. The rosin may be derived from tall oil rosin, wood rosin, gum rosin, or combinations thereof.

0028As appreciated in the art, the exact components and properties of components desired for any given ink application can vary and, therefore, routine experimentation may be required to determine the optimal components and proportions of components for a given application and desired properties.

0029The following Examples are provided to further illustrate the present invention and are not to be construed as limiting the invention in any manner.

EXAMPLE 1

0030To a 5 l flask equipped with a stirrer and reflux condenser was charged 1,480 g of toluene under a nitrogen blanket. Over the period of an hour the toluene was heated to 80°C. (This temperature level and the nitrogen blanket were maintained over the course of the reaction). Subsequently, 98.8 g of benzoyl peroxide was added to the flask. Into a 3 l beaker were charged 1,659.6 g of styrene, 198.4 g of butyl acrylate, and 127.6 g of acrylic acid. This monomer mixture was added via an addition pump to the flask over a period of 3 hours. The total charge was heated for an additional 3 hours, at which time 9.9 g of benzoyl peroxide was added. The total charge was heated for an additional hour to obtain a binder composition (BC #1) having a measured solids content of 59.1%, a Gardner-Holt viscosity of Z6-, and a capillary melting point of 132°C.

0031Comparison studies were made between this binder composition (BC#1) and Ethyl Cellulose (E/C) utilising Lithol rubine pigment base (a pigment concentrate commercially available from Sun Chemicals, Inc.). First, publication gravure printing inks letdown blends were produced by adding 25 g of JONREZ® MR-560 (JONREZ® MR-560 is a toluene-soluble calcium/zinc resinate solution used for gravure inks, commercially available from the Westvaco Corporation), 16 g of the base, and 9 g of toluene to two glass jars. The jars were then agitated for 5 minutes on a RED DEVIL Shaker in order to thoroughly mix their contents. Second, to one jar was subsequently added 6% of an Ethyl Cellulose solution (Ethyl Cellulose at 7% non-volatiles in toluene) as a control. To the other jar was added 8% of BC#1 (which had previously been reduced to a solids content of about 40% via the addition of toluene). The jars were agitated for 5 minutes to mix their contents.

0032Both ink formulations were reduced to a viscosity of 18 seconds in a #2 Shell Cup at 25°C by adding 35 ml of toluene to 50 g of the respective formulations. The inks were then drawn down and evaluated. The respective glosses were measured via a Pacific Scientific GLOSSGARD II 60° Glossmeter. The BC#1 formulation's gloss rating of 59.1 was clearly superior to the E/C formulation's rating of 46.3. Likewise, the colour intensities of the formulations were measured as B values (C. I. E. system). Again, the BC#1 formulation's rating of 35.04 was superior to the E/C formulation's rating of 30.76.

EXAMPLE 2

0033To a 5 l flask equipped with a stirrer and reflux condenser was charged 518 g of toluene under a nitrogen blanket. Over the period of an hour the toluene was heated to 80°C. (This temperature level and the nitrogen blanket were maintained over the course of the reaction). Subsequently, 31.2 g of benzoyl peroxide was added to the flask. Into a 3 l beaker were charged 580.9 g of styrene, 69.4 g of butyl acrylate, 44.7 g of acrylic acid, and 0.65 g of divinylbenzene (55%). This monomer mixture was added via an addition pump to the flask over a period of 3 hours. The total charge was heated for an additional 6 hours to obtain a binder composition (BC #2) having a measured solids content of 57.0%, a Gardner-Holt viscosity of Z6+, and a capillary melting point of 142°C.

0034Comparison studies were made between this binder composition (BC#2) and Ethyl Cellulose (E/C) utilising Lithol rubine pigment base (an ink concentrate commercially available from Sun Chemicals, Inc.). First, publication gravure printing inks letdown blends were produced by adding 25 g of JONREZ® MR-560 (JONREZ® MR-560 is a toluene-soluble calcium/zinc resinate solution used for gravure inks, commercially available from the Westvaco Corporation), 16 g of the base, and 9 g of toluene to two glass jars. The jars were then agitated for 5 minutes on a RED DEVIL Shaker in order to thoroughly mix their contents. Second, to one jar was subsequently added 6% of an Ethyl Cellulose solution (Ethyl Cellulose at 7% non-volatiles in toluene) as a control. To the other jar was added 8% of BC#2 (which had previously been reduced to a solids content of about 40% via the addition of toluene). The jars were agitated for 5 minutes to mix their contents.

0035Both ink formulations were reduced to a viscosity of 18 seconds in a #2 Shell Cup at 25°C by adding 35 ml of toluene to 50 g of the respective formulations. The inks were then drawn down and evaluated. The respective glosses were measured via a Pacific Scientific GLOSSGARD II 60° Glossmeter. The BC#2 formulation's gloss rating of 62.5 was clearly superior to the E/C formulation's rating of 46.3. Likewise, the colour intensities of the formulations were measured as B values (via the C. I. E. system). Again, the BC#2 formulation's rating of 31.52 was superior to the E/C formulation's rating of 30.76.

EXAMPLE 3

0036To a 3 l flask equipped with a stirrer and reflux condenser was charged 1,243.2 g of toluene under a nitrogen blanket. Over the period of an hour the toluene was heated to 80°C. (This temperature level and the nitrogen blanket were maintained over the course of the reaction). Subsequently, 74.9 g of benzoyl peroxide was added to the flask. Into a 1 l beaker were charged 1,394.2 g of styrene, 166.6 g of butyl acrylate, 107.3 g of acrylic acid, and 1.6 g of divinylbenzene. This monomer mixture was added via an addition pump to the flask over a period of 3 hours. The total charge was heated for an additional 5 hours to obtain a binder composition (BC #3) having a measured solids content of 39.9%, a Gardner-Holt viscosity of Y+, and a capillary melting point of 144°C.

0037Comparison studies were made between this binder composition (BC#3) and Ethyl Cellulose (E/C) utilising Lithol rubine pigment base (a pigment concentrate commercially available from Sun Chemicals, Inc.). First, publication gravure printing inks letdown blends were produced by adding 25 g of JONREZ® MR-560 (JONREZ® MR-560 is a toluene-soluble calcium/zinc resinate solution used for gravure inks, commercially available from the Westvaco Corporation), 16 g of the base, and 9 g of toluene to two glass jars. The jars were then agitated for 5 minutes on a RED DEVIL Shaker in order to thoroughly mix their contents. Second, to one jar was subsequently added 6% of an Ethyl Cellulose solution (Ethyl Cellulose at 7% non-volatiles in toluene) as a control. To the other jar was added 8% of BC#3 (which had previously been reduced to a solids content of about 40% via the addition of toluene). The jars were agitated for 5 minutes to mix their contents.

0038Both ink formulations were reduced to a viscosity of 18 seconds in a #2 Shell Cup at 25°C by adding 35 ml of toluene to 50 g of the respective formulations. The inks were then drawn down and evaluated. The respective glosses were measured via a Pacific Scientific GLOSSGARD II 60° Glossmeter. The BC#3 formulation's gloss rating of 59.6 was clearly superior to the E/C formulation's rating of 45.0. Likewise, the colour intensities of the formulations were measured as B values (via the C. I. E. system). Again, the BC#3 formulation's rating of 31.72 was superior to the E/C formulation's rating of 27.64.

EXAMPLE 4

0039To a 3 l flask equipped with a stirrer, reflux condenser, and two addition funnels was charged 600.1 g of dipropylene glycol monomethyl ether (DPM) under a nitrogen blanket. Over the period of an hour the DPM was heated to 160°C. (This temperature level and the nitrogen blanket were maintained over the course of the reaction). Subsequently, 14.6 g of di-tert-butyl peroxide was added to the flask through the first addition funnel. Into a 1 l beaker were charged 489.4 g of vinyl toluene, 58.5 g of butyl acrylate, and 38.1 g of acrylic acid. This monomer mixture was added via the second additional funnel to the flask at a rate of 5 grams per minute. Afterwards, the total charge was heated for an additional 5 hours to obtain a binder composition (BC #4).

EXAMPLE 5

0040A binder composition was made using a continuous stirred tank reactor (CSTR) via the following procedure. The weight ratio of monomers in the feed was 83.5 parts of styrene, 6.5 parts of acrylic acid, 10.0 parts of butyl acrylate, and 0.1 parts of divinyl benzene. Based on the weight of the monomers, the feed had 2.5% of di-tert-butyl peroxide as an initiator and no chain transfer agent. The reaction solvent was isopropanol at 20% by weight of the total feed (25.6% by weight of monomers).

0041The feed rate for the run was 8.0 grams per minute, which gave a residence time in the CSTR of about 125 minutes. Process temperature in the CSTR averaged 159°C on the run. Process temperature in the solvent flash vessel during the steady-state part of the run averaged 165°C and ranged from 162 to 168°C. Pressure in the solvent flash vessel was atmospheric, and the resin pump was employed to discharge the resin continuously. About 3,187 grams of a solid resin binder composition (BC#5) was produced having a number average molecular weight of about 6,270 and a ring and ball softening point of about 126.6°C.

EXAMPLE 6

0042A binder composition was made using a continuous stirred tank reactor (CSTR) via the following procedure. The weight ratio of monomers in the feed was 83.5 parts of styrene, 6.5 parts of acrylic acid, and 10.0 parts of isodecyl methacrylate. Based on the weight of the monomers, the feed had 2.5% of di-tert-butyl peroxide as an initiator and no chain transfer agent. The reaction solvent was isopropanol at 20% by weight of the total feed (25.6% by weight of monomers).

0043The feed rate for the run was such that the residence time in the CSTR of about 120 minutes. Process temperature in the CSTR averaged 158°C on the run. Process temperature in the solvent flash vessel during the steady-state part of the run ranged from 178 to 190°C. Pressure in the solvent flash vessel was atmospheric, and the resin pump was employed to discharge the resin continuously. About 2,286 grams of a solid resin binder composition (BC#6) was produced having a number average molecular weight of about 5,300 and a ring and ball softening point of about 121.5°C.

0044Many modifications and variations of the present invention will be apparent to one of ordinary skill in the art in light of the above teachings. It is therefore understood that the scope of the invention is not to be limited by the foregoing description, but rather is to be defined by the claims appended hereto.