Pigment dispersing agent and offset printing ink composition employing the same

A pigment dispersing agent comprising the reaction product of a polyester having a free carboxyl group, of which the acid value is in the range of from 10 to 60, with an amine compound of the formula: ##STR1## wherein R.sub.1 and R.sub.2 are alkylene radicals which can be the same or different, each containing from 2 to 6 carbon atoms, and R.sub.3 is a radical of the formula CH.sub.3 -- or C.sub.2 H.sub.5 --, wherein said reaction being conducted in the range of from 0.8 to 1.0 of equivalent molar ratio of the amino groups having active hydrogen of said amine compound to the free carboxyl groups of said polyester. Application of the dispersing agent to nonaqueous paint or printing inks enables pigments to be dispersed in the vehicle at higher concentrations with low viscosity than in the prior art, and the dispersions thus obtained exhibit high coloring power and excellent storage stability.

BACKGROUND OF THE INVENTION: 
1. Field of the Invention 
The present invention relates to a pigment dispersing agent that may be 
used to stably disperse an inorganic or organic pigment in a nonaqueous 
organic medium at high concentrations and also a offset printing ink 
composition employing the same. More particularly, the present invention 
pertains to a pigment dispersing agent which is capable of exhibiting 
excellent printing performance when used in an offset printing ink. 
2. Description of the Prior Art 
In general, coating agents such as printing inks and paints are prepared by 
dispersing a finely divided pigment serving as a coloring agent in a 
medium called a vehicle which consists essentially of a binder resin and a 
solvent. 
The pigment dispersion thus obtained is required to be stable without 
causing reaggregation of the pigment even after being stored for a long 
period of time and to be capable of forming a coating film which has 
excellent gloss and superior coloring properties. 
In many cases, however, pigment dispersions prepared by dispersing finely 
divided pigments in vehicles have high viscosities, so that they are 
difficult to handle in such operations as removal from a dispersion mixer, 
stirring, transportation, etc. Therefore, the pigment concentration in the 
dispersions cannot unrestrictedly be increased from the viewpoint of 
operating efficiency. 
For this reason, there is a demand for pigments that can be stably 
dispersed in vehicles at high concentrations and that permit the resulting 
dispersions to have a low level of viscosity. 
The above-described demands depend upon the pigment dispersing performance 
of the vehicle employed and it is therefore a problem of considerable 
importance to develop vehicles which enable pigments to be effectively 
dispersed therein. 
To this end, many studies have heretofore been conducted to improve binder 
resins that constitute vehicles. However, since binder resins themselves 
are polymers with high molecular weight and must maintain the important 
function of being film forming agents, the pigment dispersing performance 
thereof cannot be improved by a large margin. It is therefore actual 
practice to jointly use auxiliaries for dispersing pigments. 
These dispersing auxiliaries are, however, a group of substances which are 
called surface active agents, and many of them have relatively low 
molecular weights. When such surface active agents are employed as 
dispersing auxiliaries for nonaqueous disperse systems, electrostatic 
repulsion cannot be expected to stabilize the dispersion and the 
stabilization of the dispersion must rely solely on the steric hindrance 
by the dispersing auxiliaries adsorbed on the surfaces of pigment 
particles. Accordingly, dispersing agents having relatively low molecular 
weights are not effective in providing satisfactory dispersion stability 
and present various restrictions with respect to applicability. 
For instance, if a surface active agent having a relatively low molecular 
weight is used as a dispersing agent for an ink used in offset printing 
which is an image forming method utilizing the interfacial chemical 
repulsion that takes place between the water component, i.e., dampening 
water, and the oil component, i.e., oil-based ink, the emulsifying 
characteristics of the ink with respect to the dampening water are 
adversely affected, resulting in various problems such as scumming and 
greasing which are caused by the transfer of ink to the non-image area. 
Various kinds of dispersing agent with polymer chains which have relatively 
high molecular weights have recently been proposed for the purpose of 
ameliorating the disadvantages of the conventional dispersing agents 
having relatively low molecular weights. 
For example, Japanese Patent Publication No. 54(1079)-34009 (corresponding 
to BP 1,342,746) proposes a polyester oligomer obtained by esterification 
condensation of a hydroxycarboxylic acid, while Japanese Patent 
Publication No. 57(1982)-25251 (corresponding to BP 1,373,660) proposes a 
compound in the form of an amide obtained by carrying out reaction of the 
above-described polyester oligomer with an amine compound. 
Further, U.S. Pat. No. 4,224,212 discloses a dispersing agent comprising a 
polyester oligomer and a polyalkylene imine having molecular weight, more 
than 500, preferably 10,000-100,000, which are linked together. 
Japanese Patent Kokai (Laid-Open) No. 61(1986)-163977 discloses a reaction 
product of a polyester oligomer with either piperazine or alkyl 
piperazine. 
The proposed dispersing agents are, however, still unsatisfactory in terms 
of their achievability to high pigment concentration and dispersion 
stabilization in nonaqueous disperse systems, although they are fairly 
effective in comparison with the conventional low-molecular dispersing 
agents. When these dispersing agents are used in offset printing inks, the 
emulsifying characteristics of the inks are adversely affected to a 
significant extent, so that satisfactory print results cannot be obtained. 
Thus, the prior art dispersing agents are impractical. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a considerably 
effective and novel dispersing agent which enables a pigment to be stably 
dispersed in a nonaqueous disperse system at high concentrations and which 
will not impair the printability of offset printing inks when it is used 
as a dispersing agent therefor. 
It is another object of this invention to provide an offset printing ink 
composition employing said pigment dispersing agent. 
Other objects and advantages of this invention may become apparent to those 
skilled in the art from the following description and disclosure. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides a pigment dispersing agent comprising the 
reaction product of a polyester having a free carboxyl group, of which the 
acid value is in the range of from 10 to 60, with an amine compound of the 
formula: 
##STR2## 
wherein R.sub.1 are alkylene radicals (which can be the same or different) 
each containing from 2 to 6 carbon atoms, and R.sub.3 is a radical of the 
formula CH.sub.3 --or C.sub.2 H.sub.5 --, wherein said reaction being 
conducted in the range of from 0.8 to 1.0 of equivalent molar ratio of the 
amino groups having active hydrogen of said amine compound to the free 
carboxyl groups of said polyester. 
The present invention further provides an offset printing ink composition 
consisting essentially of a pigment, a resin, an organic solvent and any 
of the pigment dispersing agents described above in an amount of from 0.1 
to 100% by weight based on the weight of the pigment. 
The following is a comparison of the features of the dispersing agents 
according to the present invention with those according to the prior art. 
The reaction products of polyesters derived from hydroxycarboxylic acids 
with amine compounds disclosed, for example, in the specifications of 
Japanese Patent Publication No. 57(1982)-25251 (corresponding to BP 
1,373,660) have a structure wherein a tertiary amino group which serves as 
an activity point of adsorption on the pigment surfaces is present at the 
end of a polyester chain, whereas the dispersing agents according to the 
present invention have a structure wherein two polyester chains are 
usually linked with a specific amine compound and a tertiary amino group 
which serves as an adsorptive activity point is present in the center of 
the molecule, as shown by the following model: 
##STR3## 
Accordingly, the dispersing agents according to the present invention have 
a molecular weight which is about double that of the dispersing agents 
disclosed in the prior art literature and therefore the dispersal 
efficiency by steric hindrance is markedly enhanced. Thus, the dispersing 
agents of the present invention exhibit a remarkably high level of 
effectiveness in stabilizing a dispersion. 
Another of the features of the present invention resides in that, since the 
concentration of hydrophilic groups (imino groups) in the molecules is 
relatively low, there will be no adverse effects on such aspects of the 
printing performance as the emulsifiability when the dispersing agents of 
the present invention are used in offset printing inks. 
In the case of the reaction product of a polyester oligomer with either 
piperazine or 1-alkyl piperazine that is disclosed in Japanese Patent 
Kokai (Laid-Open) No. 61(1986)-163977, there is a possibility of two 
polyester chains being linked as a result of the reaction with piperazine. 
In such a case, however, from the viewpoint of the proposition of the 
reactants in the reaction there will be neither a tertiary nor a secondary 
amino group which would serve as an adsorptive activity point in the 
manner mentioned in regard to the present invention. Accordingly, the 
reaction product fails to provide satisfactory effectiveness in 
stabilizing dispersion. 
Although an adsorptive activity point is provided by the reaction with 
alkyl piperazine, since the activity point is located at the end of the 
polyester chain in the same way as in the case of the dispersing agent 
disclosed in Japanese Patent Publication No. 57(1982)-25251, the reaction 
product thus obtained is unsatisfactory in terms of dispersal efficiency 
or application for offset printing inks due to the reason mentioned above. 
The dispersing agents of the present invention exhibit desired levels of 
dispersal and printing performance owing to the special structure 
described above. 
Examples of polyesters which are usable in the present invention include 
those which are synthesized by polycondensation of compounds having 
carboxyl groups and compounds having hydroxyl groups and which have free 
carboxyl groups at the respective ends. 
Examples of dicarboxylic acids which represent one kind of material usable 
to obtain polyesters having free carboxyl groups include succinic acid, 
adipic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, 
1,2- or 1,4-cyclohexanedicarboxylic acid and terephthalic acid, etc. 
Examples of dioles which represent another kind of material usable to 
obtain polyesters having free carboxyl groups include ethylene glycol, 
diethylene glycol, propylene glycol, etc. It is possible to obtain desired 
polyesters by carrying out esterification reaction using these materials 
while taking into consideration the molar ratio thereof. 
To obtain desired dispersing agents according to the present invention, it 
is particularly preferable to employ polyesters obtained by 
polycondensation of fatty acids having hydroxyl groups. Examples of fatty 
acids having hydroxyl groups are ricinoleic acid, 12-hydroxystearic acid, 
a commercially available castor oil fatty acid containing a small amount 
of a saturated or unsaturated fatty acid, and hydrogenated fatty acids of 
this kind. To obtain desired polyesters, these materials are heated to a 
temperature of from 160.degree. to 220.degree. C. optionally with/without 
an esterification catalyst while any water formed is removed, until a 
predetermined acid value is reached. The acid value of the polyesters is 
preferably in the range of from 10 to 60, more preferably from 20 to 50. 
If the acid value is greater than 60, the length of polyester chains is 
insufficient to achieve stabilization of dispersion by an increase in 
molecular weight. Further, since the concentration of the amide groups and 
other polar groups is excessively high, the printing performance in offset 
printing will be impaired. 
If the acid value is less than 10, the concentration of groups serving as 
adsorptive activity points is excessively low. Accordingly, the 
adsorptivity of the dispersing agents on the pigment surfaces is weakened, 
and no satisfactory dispersing effect is obtained. 
Practical examples of amine compounds which react with the above-described 
polyesters to link with the polyester chains include methyl 
imino-bis-ethylamine, methyl imino-bis-propylamine, methyl 
imino-bis-butylamine, ethyl imino-bis-ethylamine, ethyl 
imino-bis-propylamine, ethyl imino-bis-butylamine, 
N-methylamino-N-ethylamino methylamine etc. In the reaction of these amine 
compounds with the above-described polyesters it is most preferable to set 
the equivalent molar ratio of the amino groups of the amine compounds to 
the free carboxyl groups of the polyesters in the range of from 0.8 to 
1.0. 
The reaction of the two materials may be carried out in the following 
manner. After the above-described polyesterification reaction has been 
completed in the range of from 160.degree. to 240.degree. C., the contents 
of the reaction system are cooled down to around 100.degree. C. Then, a 
predetermined amount of an amine compound is added thereto and the mixture 
is reheated to a temperature of from 160.degree. to 180.degree. C. to 
remove water generated by the formation of amide linkages from the 
reaction system, thereby obtaining a reaction product. 
The reaction product thus obtained may be used in the form of a salt which 
can be produced by mixing the reaction product with a desired inorganic 
acid in a range within which the equivalent amount of tertiary amine 
groups is not exceeded and heating the mixture as necessary. Examples of 
acids usable to form salts are hydrochloric acid, sulfuric acid, propionic 
acid, benzene sulfonic acid, benzoic acid, and a dyestuff or pigment 
derivative containing at least one carboxylic acid or sulfonic acid group, 
e.g., sulfonated phthalocyanine dyestuffs. Among the salts, a quarternary 
ammonium salt formed using dimethylsulfuric acid as a salt forming agent 
leads to particularly favorable results. 
Examples of solvents which may be suitably employed with the dispersing 
agents of the present invention include aromatic hydrocarbons such as 
toluene and xylene, ketone such as methyl ethyl ketone and methyl isobutyl 
ketone esters such as butyl acetate and Cellosolve acetate, and mineral 
oils which are mixtures of hydrocarbons consisting essentially of 
aliphatic hydrocarbons. 
When the dispersing agents of the present invention are used in offset 
printing ink, which is the principal use thereof, mineral oils are the 
preferred solvents. 
Pigments which are to be dispersed by the dispersing agents of the present 
invention are colorless or colored pigments. Practical examples of these 
pigments are inorganic pigments such as titanium dioxide, barium sulfate, 
calcium carbonate and magnetic iron oxide, organic pigments such as azo 
pigments, lake pigments, phthalocyanine pigments, isoindolinone pigments 
and quinacridone pigments, and carbon black. The dispersing agents of the 
present invention are effectively used to disperse oxidation-treated 
carbon black, phthalocyanine pigment, titanium dioxide, etc. among the 
pigments mentioned above. 
In the field of offset printing inks, it is common practice to prepare a 
base ink by displacing the water in a water-containing pigment cake with 
an oily vehicle by the use of a flushing means. There has in the past been 
no dispersing agent suitable for obtaining a high-concentration pigment 
base in a flushing process, especially for yellow azo pigments. The 
dispersing agents according to the present invention, however, exhibit 
excellent effectiveness in such a flushing process. It is preferred that 
the amount of dispersing agent used is in the range of from 0.1 to 100% by 
weight, more preferably from 1 to 20% by weight, based on the various 
kinds of pigment mentioned above. However, the ratio depends on the 
properties of each particular pigment used, particularly the surface area 
thereof. It is therefore necessary to determine an optimal ratio in 
accordance with the kind of pigment used. 
To produce offset printing inks using the dispersing agents according to 
the present invention, it is possible to employ various kinds of resin as 
binders, for example, known alkyd resins, rosin-modified phenolic resins 
petroleum resins, etc., and also to use other additives if necessary. 
The present invention will be further described by way of Examples. 
However, the present invention is in no way restricted by those Examples. 
Polyesters used to produce the dispersing agents of the present invention 
were prepared as follows: 
POLYESTER A 
700 gm of a commercial grade of 12-hydroxystearic acid (having hydroxyl and 
acid values of 161 mg.KOH/gm and 182 mg.KOH/gm, respectively) was charged 
into a 1000 cc flask equipped with a nitrogen gas supply pipe, a condenser 
and a water separator and melted under heating at about 100.degree. C. 
Thereafter, 70 gm of xylene and 1 gm of tetrabuthoxytitanate as a catalyst 
were added thereto, and the resulting mixture was heated to a temperature 
of from 180.degree. to 200.degree. C. The reaction was carried out for 12 
hours while water formed in the esterification reaction was separated from 
the xylene. After about 30 gm of water had been collected (equivalent to a 
degree of conversion of 90% based on the hydroxyl value). the reaction was 
suspended and the contents were cooled to obtain a light-brown, viscous 
polyester solution. The nonvolatile content of the product was 90% and the 
acid value of the solid content was 34.9 mg.KOH/gm. 
POLYESTER B 
Esterification reaction was conducted for 10 hours in the same way as in 
the case of Polyester A except that a commercially available castor oil 
fatty acid (having hydroxyl value of 163mg.KOH/gm, acid value of 181 
mg.KOH/gm) was employed to obtain a polyester solution having a 
nonvolatile content of 90%. The acid value of the solid content was 43.5 
mg.KOH/gm.

EXAMPLE 1: PREATION OF DISPERSING AGENT A 
300 gm of Polyester A and 11.5 gm of methyl-imino-bis-propylamine 
(corresponding to 0.95 equivalent with respect to the acid value of the 
polyester) were charged into a 500 cc flask similar to that employed for 
the esterification reaction. The reaction was carried out at a temperature 
of from 160.degree. to 180.degree. C. while water generated by the 
formation of amide linkages was separated from the xylene. After 80% of 
water based on the stoichiometric quantity had been collected, xylene was 
distilled off under reduced pressure. 
The resulting product was a light-brown, slightly turbid, viscous liquid. 
According to gel permeation chromatography, the molecular weight of the 
product was 3,500. The amine value was 16.5 mg.KOH/gm, while the acid 
value was 7.3 mg.KOH/gm. 
EXAMPLE 2: PREATION OF DISPERSING AGENT B 
The same procedure as in Example 1 was carried out except that 300 gm of 
Polyester B and 12.1 gm of methyl imino-bis-propylamine (corresponding to 
0.9 equivalent with respect to the acid value of the polyester) were used, 
thereby obtaining a light-brown, transparent, viscous liquid having a 
molecular weight of 3,000, an amine value of 17.8 mg.KOH/gm and an acid 
value of 9.2 mg.KOH/gm. 
EXAMPLE 3: PREATION OF DISPERSING AGENT C 
The same procedure as in Example 1 was carried out except that 300 gm of 
Polyester A and 14.0 gm of methyl imino-bis-butylamine (corresponding to 
0.95 equivalent with respect to the acid value of the polyester) were 
used. thereby obtaining a light-brown, slightly turbid, viscous liquid 
having a molecular weight of 4,800, an amine value of 11.3 mg.KOH/gm and 
an acid value of 6.4 mg.KOH/gm. 
EXAMPLE 4: PREATION OF DISPERSING AGENT D 
3.6 gm of dimethylsulfuric acid (corresponding to 0.98 equivalent with 
respect to the amine value) was added to 100 gm of the product obtained in 
Example 1 and the resulting mixture was heated for 1 hour at 90 to 
100.degree. C. thereby converting the alkylimino groups to quarternary 
ammonium salt groups. Infra-red spectroscopic analysis of the product 
showed absorption bands at 750 and 1015 cm.sup.-1 due to the presence of a 
"CH.sub.3 SO.sub.4 " anion. The amine value of the produce was not greater 
than 1. 
COMATIVE EXAMPLE 1: PREATION OF DISPERSING AGENT E 
The same procedure as in Example 1 was carried out except that 300 gm of 
Polyester A and 6.9 gm of N,N-dimethylaminopropylenediamine (corresponding 
to 0.95 equivalent with respect to the acid value of the polyester) were 
used, thereby obtaining a light-brown, wax-like product having a molecular 
weight of 1,800, an amine value of 35.5 mg.KOH/gm and an acid value of 
14.2 mg.KOH/gm. 
COMATIVE EXAMPLE 2: PREATION OF DISPERSING AGENT F 
7.8 gm of dimethylsulfuric acid (corresponding to 0.98 equivalent with 
respect to the imino group) was added to 100 gm of the product obtained in 
Comparative Example 1 and the resulting mixture was heated for 1 hour at 
90 to 100.degree. C. thereby converting the tertiary amino groups to 
quarternary ammonium salt groups. Infra-red spectroscopic analysis of the 
product showed absorption bands at 750 and 1015 cm.sup.-1 due to the 
presence of a CH.sub.3 SO.sub.4 anion. The amine value of the product was 
not greater than 1, 
PERFORMANCE EVALUATION TEST 1 
Master bases for offset inks and offset inks were prepared according to the 
following formulations using the dispersing agents shown in Examples 1 to 
4 and Comparative Examples 1 and 2. The properties and performances of the 
prepared master bases and offset inks are shown in Table 1. 
It should be noted that Comparative Example 3 shown in Table 1 is an 
example in which no dispersing agent gas used. 
______________________________________ 
Indigo blue master base 
Phthalocyanine blue 50 parts 
Dispersing agent 5 parts 
Alkyd resin (Beckosol 8011, manufactured by 
10 parts 
Dainippon Ink & Chemical Company) 
Rosin-modified phenolic resin varnish* 
10 parts 
Solvent No. 5 (manufactured by Nippon Oil 
25 parts 
Company, Limited) 
Black master base 
Carbon black 50 parts 
Dispersing agent 5 parts 
Alkyd resin 10 parts 
Rosin-modified phenolic resin varnish 
10 parts 
Solvent No. 5 25 parts 
______________________________________ 
Each of the above-described compositions was thoroughly mixed and milled 
using a three-roll mill to prepare a master base and an offset ink was 
obtained according to the following formulation: 
______________________________________ 
Master base 35 parts 
Rosin-modified phenolic resin varnish* 
50 parts 
Fluorine wax 2 parts 
Cobalt naphthelate (Co: 6%) 
1 part 
Solvent No. 5 12 parts 
______________________________________ 
*It should be noted that the abovedescribed varnish was prepared by 
uniformly dissolving under heating to 220.degree. C., 40 parts of 
rosinmodified phenolic resin (Hitanol 271A available from Hitachi Chemica 
Co. Ltd.), 25 parts of linseed oil and 35 parts of Solvent No. 5. 
TABLE 1 
__________________________________________________________________________ 
Comp. Comp. Comp. 
No. Example 1 
Example 2 
Example 3 
Example 4 
Example 1 
Example 2 
Example 
__________________________________________________________________________ 
3 
Dispersing 
Agent a Agent b Agent c Agent d Agent e Agent f None 
Agents (Note 1) 
Inks Indigo 
Black 
Indigo 
Black 
Indigo 
Black 
Indigo 
Black 
Indigo 
Black 
Indigo 
Black 
Indigo 
Black 
blue blue blue blue blue blue blue 
Master 
base 
Viscos- 
250 170 275 180 220 175 310 190 680 375 540 350 Impossible 
ity to mill 
Color- 115 108 112 106 116 106 114 105 105 103 107 102 100 100 
ing 
power 
Storage 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
stabil- 
ity 
Ink 
Gloss .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
Print- .circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.circle. 
.DELTA. 
.DELTA. 
.DELTA. 
.DELTA. 
.circle. 
.circle. 
ing per- 
formance 
__________________________________________________________________________ 
Note 1 in Table 1 denotes that attempts were made to prepare a master base 
according to the same formulation except that 5 parts of alkyd resin were 
employed in place of 5 parts of dispersing agent, but it was impossible to 
effect milling: therefore, an ink was prepared using a base having a 
pigment concentration of 25%. 
The performance was evaluated according to the following methods: 
Viscosity: Viscosity (poise) at 25.degree. C. was measured using a Larey 
viscometer. 
Coloring power: Coloring power with respect to white ink was measured on 
the basis of the coloring power in Comparative Example 3 and shown in %. 
Storage stability: Each master base was stored for 1 month in a constant 
temperature bath at 25.degree. C. and the viscosity measured at that time 
was compared with the viscosity of the master base when prepared ( 
.circleincircle.=excellent, .circle.=good and .DELTA.=inferior). 
Gloss: Gloss of print was judged by visual observation ( 
.circleincircle.=excellent, .circle.=good and .DELTA.=inferior) 
Printing performance: Printing was actually performed with a sheet-feed 
offset press manufactured by Mitsubishi Heavy Industries, Limited and such 
aspects as water allowance, ink transfer ratio, scumming and greasing were 
judged synthetically ( .circleincircle.=excellent, .circle.=good, 
.DELTA.=inferior). 
PERFORMANCE EVALUATION TEST 2 
The following composition was charged into a small-sized flusher and water 
was completely separated by an ordinary flushing process, thereby 
displacing water with an oily vehicle. 
______________________________________ 
Composition: 
Water-containing cake (piment content: 
1600 parts 
25%) of a yellow azo piment (Cl.PIG.No.12) 
Dispersing Agent a 50 parts 
Alkyd resin 100 parts 
Rosin-modified phenolic resin varnish 
100 parts 
Solvent No. 5 350 parts 
______________________________________ 
By this process, a base ink having an extremely high pigment concentration 
(40%) and a considerably low viscosity was obtained. The ink that was 
obtained from this base had a coloring power of 103% in comparison with 
the products obtained by the conventional method. 
It should be noted that, when flushing was carried out without using a 
dispersing agent, the concentration limit of the yellow azo pigment base 
was 25%. 
PERFORMANCE EVALUATION TEST 3 
A master base having a pigment concentration of 40% was obtained using the 
same formulation as in the performance evaluation test 2 except that 
Dispersing Agent e obtained in Comparative Example 1 was employed in place 
of Dispersing Agent a. 
The resulting master base had a higher viscosity than that of the base ink 
obtained in the performance evaluation test 2 and the coloring power of 
this master base was low, i.e., 78% of that of the conventional products. 
Application of the dispersing agents according to the present invention to 
nonaqueous paint of printing inks enables pigments to be dispersed in the 
vehicle at a higher concentration than in the prior art, and the 
dispersions thus obtained exhibit high coloring power and excellent 
storage stability. As a result, it is possible to increase the operation 
efficiency by a large margin and also to reduce storage and transportation 
costs, In particular, when the dispersing agents of the present invention 
are applied to offset inks preparation of high-concentration master bases 
is enabled without adverse effects on the printing performance of the kind 
previously experienced with the conventional dispersing agents.