Rosin-Based Grind Resins for Aqueous Printing Inks

The invention relates to compositions of matter for ink pigment grinding resins and the process for preparing them. In particular, the invention relates to grinding resins which produce high solids pigment dispersions for stable water-based ink formulations.

Impelled by environmental concerns and increasing governmental regulations on the volatile organic content of inks and coatings, the applications of water-based flexographic and rotogravure inks are increasing in the ink industry. A typical water-based ink system is formulated by the addition of a binder resin (usually acrylic polymer lattices) to a grind base. Grind bases are prepared by using grinding resins to disperse pigments. Pigments are crystalline solids composed of agglomerates, aggregates, and primary particles which vary in size from 0.02 to 0.5 microns. During the grinding process, agglomerates and aggregates are broken down into primary particles which possess strong tendencies to reassociate in an ink. The finer the particle size of the pigment, the greater the color strength, but the more difficult the pigment becomes to disperse. Grinding resins help prevent the particles from reassociating by increasing both the electrostatic and steric repulsion between pigment particles.

An ink formulator must consider the compatibility of the various ink components when selecting the grind resins to be used. Grind bases (i.e., pigment dispersions) are let down with a variety of alkali-soluble resins or alkali-insoluble resin emulsions to achieve the properties desired for the end use of the ink. If the grind resins and the let-down resins are not compatible, the result may be pigment flocculation, viscosity increase, loss of color strength, and other problems.

Currently, the rosin resin FILTREZ.RTM. 5014 (manufactured by Akzo Chemicals, Inc.) is preferred in the alkali-soluble grind resin market. This resin has the ability to produce stable low viscosity grind bases and inks for water-based flexographic printing. FILTREZ 5014 also yields excellent color development when grinding pigments and contributes to the toughness and water resistance of finished inks. However, both the viscosity and the stability of grind bases and inks produced with the aid of commercially available polyester resins are highly dependent on the pigment-to-resin ratio, pigment loading, and pH-value. As grind bases must remain stable and fluid to be applicable, this pH dependence has remained a problem associated with the use of these resins.

In commonly assigned U.S. Pat. No. 5,066,331, Dr. G. Frederick Hutter describes the production of water-soluble resins having superior adhesive properties for use in formulating packaging inks. These resins are produced by reacting fumarated or maleated rosin with a compound containing two secondary amine groups and no primary amine groups. As Dr. Hutter states in the patent (Col. 2, lines 59-66), it is essential to his invention that primary amine groups not be utilized in the reaction with the modified rosin. While these resins make excellent binder resins for water based packaging inks, the resins are less successful when employed as grinding resins. Indeed, when one attempts to employ these resins as grinding resins, the resulting pigment dispersions are thixotrophic and extremely difficult to handle and utilize.

At the present time, the majority of water-based printing inks are produced at pH values between 8.5 and 10.5. It would be advantageous to ink formulators to have a resin which is stable over this entire range. Therefore, it is the object of this invention to have an alkali-soluble resin which may be used to prepare stable, low viscosity pigment dispersions over a wide range of pH values while maintaining excellent physical properties in the finished inks.

The object of this invention is met by reacting rosin with maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, or fumaric acid to produce a fortified rosin containing polycarboxylic acids (e.g., tricarboxylic acids) or polycarboxylic acid anhydrides. The fumarized (or maleinized) rosin is reacted with a polyamine containing at least one primary amine group to produce the water soluble polyimido-, polyamido-, or polyaminoamidoimide grinding resins. Since grinding resins disperse pigment and influence ink rheology, they are major components in most aqueous ink formulations. Efficient dispersion of the pigment (which is the most expensive component of ink) produces maximum color strength and prevents settling and flocculation. This in turn influences grinding efficiency, transfer, and printability.

The ratio of rosin to maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, or fumaric acid required to produce the desired polycarboxylic acid or anhydride ranges from 100:15 to 100:25. The ratio of polycarboxylic acid or anhydride to polyamine required to produce the desired grinding resin ranges from 100:10 to 100:15.

It has been found that the condensation reaction products of polyamines with certain rosin-based polycarboxylic acids or anhydrides are extremely efficient grinding aids. Grinding aids were prepared which gave good pigment dispersions at pigment-to-dispersant ratios of 5:1-15:1, and at pigment concentrations of 30-45%.

As mentioned, the invention is directed to ink pigment grinding resins and the process for preparing them. In addition, the invention is also directed to ink vehicles and inks containing such resins.

Rosin is mainly a mixture of C.sub.20, fused-ring, monocarboxylic acids, typified by levopimaric and abietic acids, both of which are susceptible to numerous chemical transformations. It is generally known in the art that .alpha., .beta.-unsaturated acids and their anhydrides, such as maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, and fumaric acid may be reacted with abietic type rosin acids to yield C.sub.24 polycyclic tricarboxylic acids and anhydrides.

The invention resin is produced by reacting rosin with maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, or fumaric acid to produce a rosin-based polycarboxylic acid or anhydride. The rosin polycarboxylic acid or anhydride is reacted with a polyamine containing at least one primary amine group to produce the alkali soluble polyamine-crosslinked grinding resin.

The polycarboxylic acids and anhydrides used in the preparation of the invention grinding aids are represented by the following formulae: ##STR1##

When the polycarboxylic acids (I) or anhydrides (II) are heated with a polyamine, a variety of condensation products (i.e., amidoamides and imidoamides) can be obtained. As a general example, the reaction products of fumarized or maleinized rosin with two preferred polyamines (aminoethylpiperazine and triethylene tetramine) are described. Aminoethylpiperazine (or AEP, shown in FIG. 1 below), contains one primary (N'), one secondary (N''), and one tertiary (N''') amine group, each of which show differences in reactivity with carboxylic acid groups when forming amides. The primary amine group is more reactive than the secondary, while the tertiary nitrogen has little or no reactivity. ##STR2##

Fumarized (or maleinized) rosin contain carboxylic groups which also show differences in reactivity. The carboxylic groups (or anhydride structures) incorporated via the Diels-Alder reaction with fumaric acid or maleic anhydride form amide- or imide- structures at lower temperatures than the original carboxyl groups of the rosin. Thus, reaction of one mole tricarboxylic acid with one mole aminoethylpiperazine will result in an aminoimido carboxylic acid (FIG. 2) at low temperature (150.degree.-160.degree. C.). ##STR3## The resulting products resemble C.sub.30 N.sub.3 -diamino imido carboxylic acids (with a carbon to nitrogen ratio of 10:1).

Reaction of one mole dicarboxylic acid with 0.5 mole aminoethylpiperazine at 240.degree.-250.degree. C. will result in tricarboxylic acids (FIG. 3). ##STR4## Here, the resulting products resemble C.sub.54 N.sub.3 -amino amido imido tricarboxylic acids (with a carbon to nitrogen ratio of 19:1).

The commercial blend consists of 4 isomers with nitrogens of various reactivities. ##STR5##

With Triethylene tetramine (only one isomer prepared with linear TETA shown). ##STR6## The resulting products resemble C.sub.54 N.sub.4 -di-amino di-imido dicarboxylic acids (with a carbon to nitrogen ratio of 13.5:1). Preferential reaction of the primary amine groups of the linear isomer with the anhydride functionalities of maleated rosin yields a alkali soluble polyamine-crosslinked dicarboxylic acid when reacted for 1-3 hours at a temperature range of 240.degree.-260.degree. C. The formaldehyde and the rosin is conducted at a temperature in the range of about 120.degree.-160.degree. C., with the preferred range being about 130.degree.-150.degree. C. The cycloaddition reaction is conducted at a temperature in the range of about 170.degree.-230.degree. C., with the preferred range being about 190.degree.-210.degree. C. The condensation reaction is conducted at a temperature in the range of about 220.degree.-280.degree. C. ,with the preferred range being about 230.degree.-60.degree. C. It is well within the expertise of a skilled artisan to vary the temperatures of and the reaction times of different reactions in order to produce the desired product.

The above reaction products constitute poly-rosin amino amido imido carboxylic acids. Fumarized (or maleinized) rosin contains carboxylic groups which also show differences in reactivity. The reaction products formed are due to the difference in reactivity of the various types of amine groups and carboxyl groups.

The ratio of tertiary amine groups to unreacted carboxylic groups can be varied as needed. One method is to decrease the number of both carboxyl groups and amine groups by blending increasing amounts of bis-primary-diamines (i.e., H.sub.2 N(CH.sub.2).sub.x NH.sub.2, etc.) to AEP (decreasing the carboxyl groups and amino groups). Another method is to decrease the number of amine groups while increasing the carboxyl groups by adding bis-secondary-diamines (i.e., CH.sub.3 NH(CH.sub.2).sub.x NHCH.sub.3, etc.) to AEP to achieve the desired piperazines.

Rosins which are suitable for use in the reaction include, but are not limited to, the following:

tall oil rosin,

wood rosin, and

gum rosin.

Reactants which are suitable for use in the Diels-Alder or the "ene"-cyclocondensation reaction with the above resin acids containing rosins include, but are not limited to, the following:

acrylic acid,

methacrylic acid,

fumaric acid, and

maleic anhydride.

Polyamines which are suitable for use in the reaction must have at least one primary amine group and include, but are not limited to, the following:

ethylene diamine,

diethylene triamine,

triethylene tetramine,

tetraethylene pentamine,

pentaethylene hexamine (and higher homologous),

N-aminoethyl propane diamine,

N-aminoethyl substituted butane diamines,

pentane diamines,

hexane diamines,

N-hydroxy ethyl ethylene diamine,

1,3-diaminopropane,

1,4-diaminobutane,

1,5-diaminopentane,

1,6-diaminohexane,

N-aminoethylpiperazine,

N-hydroxyethyl piperazine,

N-aminopropyl-propane diamine-1,3,

N-methyl-N-aminopropylpropane diamine-1,3,

N-aminohexylhexane diamine-1,6,

aminoethylethanolamine,

bis-aminopropylamine,

pentamethylenediamine, and

AMINE HH.

AMINE HH.RTM. (a polyamine blend manufactured by Union Carbide, Inc.) is composed of the following major ingredients:

The grind bases and inks produced from the invention grinding aid are suitable for use within the pH range of 8.5 to 10.5.

As 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 optional components and proportions of components for a given application and desired properties.

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

A grinding aid for pigments used in water-based printing inks was produced via the following procedure. All reactants are measured in parts by weight.

One hundred (100) parts of ROSIN SS.RTM. (a tall oil based rosin manufactured by Westvaco, Inc. was heated to 210.degree. C. under a positive nitrogen pressure. Fifteen (15) parts of fumaric acid was added in a single portion to the hot resin. The mixture was stirred at 210.degree. C. for 2 hours. Over a period of 30 minutes 8.6 parts of aminoethylpiperazine (AEP) was slowly added to the adduct, and heated to 240.degree. C. (until all water of condensation was removed). The product was allowed to cool and the resin collected. For final pH adjustment of the aqueous varnishes, the desired amount of NH.sub.3 or an amine was used. Finally, 0.1-1 part of FOAMBLAST 327.RTM. (a defoamer manufactured by Ross Chemicals, Inc.) was added.

A series of grinding resins was produced (via the method taught in Example 1) by reacting ROSIN SS with increasing amounts of fumaric acid or maleic anhydride (from 15-25%) and 0.25-0.50 mole equivalents of aminoethylpiperazine (AEP) or triethylenetetramine (TETA) based on fumaric acid or maleic anhydride to achieve 50% or 100% crosslinking of the fortified rosin molecules. The compositions of the various resins are listed in Table I below.

Two types of water based varnishes were prepared at a pH range of 9.0-9.5 from each respective resin. Formula A is representative of varnishes made for flexographic publication inks (at 30% NV or non-volatile), while Formula B is representative of varnishes made for flexographic packaging inks (at 35% NV).

Table I shows the properties of the varnishes after one month's storage at ambient temperature. Overall, the TETA based resins were more stable than the AEP-crosslinked resins (i.e., all the TETA varnishes remained clear).

In preparing the resins, it was found that fortification of rosin with 20% maleic anhydride is the maximum preferred level when full crosslinking is desired. If rosin is fortified with 25% maleic anhydride, only 50% crosslinking is possible without producing a high-viscosity aqueous varnish. A higher TETA-charge will produce a resin with a very high melting point and low solubility (low acid number) which may prove difficult to process. Triethylene tetramine forms resins with higher molecular weights (when compared with AEP) due to its higher number of primary and secondary amine groups.

Grind bases containing 25% and 40% phthalocyanine blue pigment presscake (manufactured by Sun Chemical, Inc. under the designation 449-550) were prepared (using the corresponding varnishes listed on page 12) at various resin contents to measure the effect of resin content on viscosity. The grind bases were formulated as follows:

(SURFYNOL DF-75.RTM. is a defoamer manufactured by Air products, Inc.) The storage stabilities of the 40% grind bases over a period of one month were evaluated against some standard industry resins (see Table II).

Inks were prepared from grind bases containing 25% pigment as follows:

(JONCRYL 87.RTM. is an acrylic resin and JONWAX 26.RTM. is a micro wax manufactured by S. C. Johnson and Sons, Inc.) (SURFYNOL 104E.RTM. is a defoamer manufactured by Air Products, Inc.) Inks were stored for at least one month to determine storage stability via viscosity measurements. The results of the screening experiments are compiled in Table II.

FILTREZ 5014 gave the lowest viscosity grind bases at 25% pigment an high resin contents; grind bases prepared at 40% pigment and 4% resin were very viscous and did not flow. The invention rosin resin gave high viscosity grind bases at high resin contents and low viscosities at low resin contents. The grind bases produced via the taught method at 40% pigment loading had good color values, comparable or better than those prepared with the resins JONCRYL 678, SURFYNOL GA, or SURFYNOL CT-135 (which are commonly used for high pigment grinds).

Taking the viscosities of the full strength inks, the 40% pigment concentrates, and the color strength of the latter into account, resin number 13 (prepared by reacting 100 parts ROSIN SS with 20 parts maleic anhydride and 14.6 parts triethylene tetramine) is a more preferred embodiment.

As carbon black is the most widely used pigment in publication flexographic inks, a series of resins were produced via the method taught in Example 1 using VULCAN K.RTM. (a carbon black manufactured by Cabot Chemicals, Inc.). Two sets of varnishes at 30% resin content were prepared: in the first set monoethanolamine was added to reach a pH range of 9.2-9.5, while the second set was prepared by dissolving 100 parts resin in the presence of 13.3 parts monoethanolamine (which resulted in high pH varnishes). Due to the low acid numbers and the partially amphoteric character of the resins, the varnishes had very high viscosities at the lower pH values. The higher amine content (pH 10.0-10.5) made the varnishes more fluid. News inks are generally prepared at a pH of approximately 10.0, thus the high pH values of the varnishes are acceptable. Also, the higher amount of monoethanolamine improves the rewetability of the inks.

The amino resins produced stable varnishes as long as the degree of maleinization is higher than 15% and the amount of amine applied for crosslinking is at least 12%. This is in contrast to many varnishes currently prepared from several commercial rosin-based polyester resins where gelation occurs on storage.

The grind bases with Vulcan K were prepared as follows (in parts by weight):

The viscosity of each was determined one day after grinding and again after at least 30 days storage. Grinds which did not change viscosities (as measured by a Shell #3 cup) by more than 5 seconds were considered stable. Due to the low resin content light settling of the pigment occurred in several cases, but the sediment could be redispersed with slight agitation.

The results are shown in Table III.

Both aminoethylpiperazine (AEP) and triethylene-tetramine (TETA) performed well as crosslinking agents. The resins prepared with TETA showed good results independent of the amount of fumaric acid or maleic anhydride used. However, a minimum amount of 12% TETA was necessary to obtain stable, noncrystallizing varnishes when prepared with water and monoethanolamine. Typical grinding aids such as SURFYNOL GA and SURFYNOL CT-136, and acrylic grind resins such as JONCRYL 678 gave low viscosity concentrates with 30% pigment at 3% resin content. However, FILTREZ 5014, which is widely used in packaging inks at higher resin loadings, produced thixotropic grinds.

In order to evaluate the color and gloss of the carbon black concentrates, the grind bases were diluted to 20% pigment concentration and drawn-down on uncoated paper with a Meyer #2 rod. The tinctorial strength was determined with a MacBeth Color Eye against the black tile for reference. The results are listed in Table IV below. A lower number indicates a darker draw-down. Gloss was determined at the 60.degree. angle.

The pH value of the grind bases prepared with the amino resins influences these values. Low pH value (7.8-8.6) grind bases gave low gloss draw-downs with high color values, whereas grind bases prepared at pH 8.7-9.5 gave higher gloss draw-downs with lower color values.

Bleaches with a TiO.sub.2 ink (FLEXOVERSE WHITE.RTM. manufactured by Sun Chemicals, Inc. under the designation WFD-5006) were prepared at a weight ratio of 19:1 from a few grind bases which showed large differences in gloss and color strength at different pH values. Due to the excess of white ink, the gloss of the draw-downs is determined by the resin of the white ink. Differences in color values are due to "true" differences in color strength of the grind bases.

As Table V below shows, grind bases prepared at the lower pH values gave darker bleach draw-downs.

A preferred grinding resin for use in preparing water-based printing inks is produced via the following procedure, which is taught in parts by weight of reactants. ROSIN SS (100 parts) was heated to 210.degree. C. in a 1000 ml three-neck round-bottom flask under a positive nitrogen flow. Maleic anhydride (24 parts) was added to the molten rosin and this mixture was stirred for three hours. A mixture of (7 parts) diethylene glycol and (7 parts) AMINE HH was added slowly and stirred at 240.degree. C. (until all water of condensation was removed). Finally, the product was allowed to cool before collecting the resin.

A series of preferred pigment grinding resins for use in preparing water-based printing inks was produced via the method taught in Example 4. Subsequently, these resins were used to produce two groups of varnishes. In one (Varnish A), 35% NV varnishes were prepared with water/isopropanol mixtures using ammonia. In the other (Varnish B), 30% NV varnishes were prepared with water only using monoethanolamine (MEA) as a base. The formulations are listed below:

All-water varnishes are generally used for publication flexography.

These varnishes were used with phthalocyanine to produce grinding bases. The phthalocyanine was ground at 25% loading using 5.25% to 10.5% grind resin as follows:

The viscosity of the grind bases are evaluated in Table VI.

Table VI shows the viscosity of the grind bases. The A resins (the resins prepared with TETA) and the B resins (the resins prepared with AMINE HH) gave storage-stable grinds up to 10.5% resin in both all-water and water/i-propanol systems. The C resins (the resins prepared with aminoethylpiperazine) gave storage-stable grinds in the all-water system but unstable gelling grinds in the water/i-propanol system. A major factor for this behavior is the higher acid number of the C resins (AN 121.8). Since the same amounts of NH.sub.3 or monoethanolamine were used for each varnish, the pH values of the grind bases containing 8.7% resins were 9.41, 9.0, 8.42 (NH.sub.3) and 10.44, 10.36, 10.26 (MEA), respectively. A pH value of 8.4 for the C resins' varnish appears to be too low. The D resins (the resins prepared with JONCRYL-678 gave stable grinds at lower viscosity. Table VII evaluates color strength and gloss of the 25% pigment grinds prepared with 8.75% resin.

At 8.75% resin content (as shown above in Table VII), the grind base prepared with the A resins had the best color strength in both the all-water and water/i-propanol system. The pH value did not influence the color development. The A and B resins (also the C-2 resin) in water/i-propanol showed better grinding efficiency (faster) than the D resins (JONCRYL-678), the hard acrylic grind resins widely used for water-based inks.

A preferred grinding aid for pigments used in water-based printing inks was produced via the following procedure. All reactants are measured in parts by weight.

One hundred (100) parts of ROSIN SS.RTM. was heated to C under positive nitrogen pressure. One (1) part of paraformaldehyde was added to the rosin, and the resulting mixture was heated to 150.degree. C. and maintained at that temperature for one hour. Fifteen (15) parts of maleic anhydride was added to the adduct, which was subsequently heated to 200.degree. C. and maintained at that temperature, with stirring, for two hours. Over a period of minutes 9.8 parts of aminoethylpiperazine (AEP) was slowly added to the adduct. The adduct was heated to 240.degree. C. and maintained at that temperature for two hours (or until all water of condensation was removed). The product was allowed to cool and the resin collected. A high pH varnish was prepared by dissolving 100 parts of the resin in 13.3 parts of monoethanolamine. This varnish was used to produce a grind by mixing 10 parts of the varnish with 30 parts of VULKAN K, 1 part of FOAMBURST 338, and 59 parts water.

Using a #3 Shell Cup, the viscosity was measured at 21.9 seconds one day after grinding and at 23.5 seconds 34 days after grinding. This is considered to be a stable grind.

A series of preferred grinding resins was produced via the method taught in Example 6 above. In each resin 100 parts of ROSIN SS was first reacted with 1 part of para-formaldehyde. The resulting adduct was in turn reacted with various amounts of maleic anhydride and aminoethylpiperazine to produce the grinding resins. The specific formulations are listed in Table VIII

High pH varnishes were prepared by dissolving 100 parts of each resin in 13.3 parts of monoethanolamine. These varnishes were used to produce grinds by mixing 10 parts of each respective varnish with 30 parts of VULKAN K, 1 part of FOAMBURST 338, and 59 parts water. The viscosities were determined one day after grinding and after at least 30 days storage, and the results listed in Table VIII below. Grinds which did not change S-3 viscosities (Shell Cup #3) by more than 5 seconds are considered stable.

Many 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.