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Journal of Oleo ScienceCopyright ©2013 by Japan Oil Chemists’ SocietyJ. Oleo Sci. 62, (6) 345-352 (2013)

Development of Solvent-Free Offset Ink Using Vegetable Oil Esters and High Molecular-Weight ResinJung Min Park1, Young Han Kim2＊ and Sung Bin Kim3

1 Kwang Myung Ink Mfg. Co., (1534-1 Sonjeong-dong, Kangseo-gu, Pusan 618-817, KOREA)2 Department of Chemical Engineering, Dong-A University, (840 Hadan-dong, Saha-gu, Pusan, 604-714, KOREA)3 Department of Graphic Arts Engineering, Pukyong National University, (365 Shinseon-ro, Nam-gu, Pusan, 608-739, KOREA)

1 IntroductionWith the recent emergence of environmental issues, the

interest in eco-friendly printing is steadily increased. In particular, for the sustainability improvement of printing inks composed of mostly petrochemical and organic chemi-cal products, eco-friendly technologies have been applied such as the development of aromatic-free and VOC（volatile organic compound）-free inks. If the petroleum-based sol-vents in the inks are replaced with the eco-friendly vegeta-ble oil or vegetable esters, the use of VOCs will be reduced and the benefits of renewable resources can be yielded1－4）. But the application of vegetable oil is limited due to its high viscosity and solubility, and the set-off problem due to the slow drying time has not been solved yet. Vegetable esters can handle the problems of the existing eco-friendly print-ing inks, because its kinematic viscosity is similar to that of petroleum-based solvents and its resin dilution power is adjustable5）. Applying soy-oil fatty acid methyl ester（FAME）directly to printing inks, however, reduces the vis-coelasticity of the inks due to its low viscosity and high resin dilution power, but causes such problems as misting and deterioration6）. For lithographic inks, in particular, emulsification, printability, and the rheological properties are important factors to be controlled, when vegetable

＊Correspondence to: Young Han Kim, Department of Chemical Engineering, Dong-A University, 840 Hadan-dong, Saha-gu, Pusan, 604-714, KOREAE-mail: yhkim@mail.donga.ac.krAccepted January 19, 2013 (received for review December 4, 2012)Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 onlinehttp://www.jstage.jst.go.jp/browse/jos/　　http://mc.manusriptcentral.com/jjocs

ester is used7－11）. To solve the problem, a proper offset-ink formulation has been sought by changing the characteris-tics of rosin-modified phenolic resin, when vegetable esters were applied12, 13）.

In this study the soy-oil FAME is applied to five types of resins with different molecular weights and solubility, to develop the eco-friendly varnish and ink. The property changes from the application are examined to find the best formulation for the ink. Furthermore, the ethyl and butyl esters of the soy oil fatty acid having high molecular weight and viscosity are used, and their resin dilution power is ad-justed to produce an eco-friendly solvent, more appropri-ate for the offset ink. The molecular weight, solubility, and other properties including rheological characteristic of the soy-oil fatty acid esters are measured, and the properties and printability of the inks are examined to determine the best formulation.

2 Experimental2.1 Materials

Five types of rosin-modified phenolic resins（Kangnam Chemical Co., Korea）with different molecular weights and

Abstract: In the development of solvent-free offset ink, the roles of resin molecular weight and used solvent on the ink performance were evaluated by examining the relationship between the various properties of resin and solvent and print quality. To find the best performing resin, the soy-oil fatty acid methyl ester (FAME) was applied to the five modified-phenolic resins having different molecular weights. It is found from the experimental results that the ink made of higher molecular weight and better solubility resin gives better printability and print quality. It is because larger molecular weight resin with better solubility gives higher rate of ink transfer. From the ink application of different esters to high molecular weight resin, the best printing performance was yielded from the soy-oil fatty acid butyl ester (FABE). It is due to its high kinematic viscosity resulting in the smallest change of ink transfer weight upon multiple number of printing, which improves the stability of ink quality.

Key words: Offset Ink, Vegetable Ester, Rosin-Modified Phenolic Resin, Printability, Rheology

J. M. Park, Y. H. Kim and S. B. Kim

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solubility were used as resin, and soybean oil（CJ Co., Korea）was applied as vegetable oil. Solvents were hydro-treated light paraffinic distillate（Techsol-2836i, GS Caltex Co., Korea）and soy oil esters－ FAME（fatty acid methyl ester）, FAEE（fatty acid ethyl ester）, and FABE（fatty acid butyl ester）（Valvoline, Korea）. For the ink preparation, phthalocyanine Beta Blue（CI Pigment Blue 15:3, Heliogen Blue D 7095, BASF, Korea）was used as pigment, and calcium carbonate（CI Pigment White 18, Hakuenka CC, Shiraishi, Japan）was added as extender.

2.2 Preparation of varnishThe varnish was formulated as the composition given in

Table 1. To maintain the viscosity in a similar level, the resin, ester, and solvent contents were varied after consid-ering the viscosity and solubility of the vegetable esters.

2.3 Preparation of inksThe inks were prepared in the composition listed in

Table 2. To make the tack and viscosity level similar, the quantities of the hydrocarbon solvents were set at 5％ point higher than those of the vegetable esters.

2.4 Instrumental analysisTo determine the molecular weight distribution of the

rosin-modified phenolic resin and soy-oil fatty acid ester, an HPLC（Agilent Technologies Co., U. S. A., Model 1200 Series）was used, and the cloud point related to the resin solubility was measured with a cloud point tester（Novo-control GmbH, Germany, Model Chemotronic II）. The emulsification was measured using an emulsification tester（Novocontrol GmbH, Germany, Model Lithotronic II）, and

the rheological properties were measured using a rheome-ter（Thermo Fisher Scientific Inc., Germany, Model Haake Mars II）. The emulsification was measured with the sample of 25 g placed in the sample holder, and the spindle was rotated at the speed of 1,200 rpm while water was supplied at the rate of 2 g/min. The measured torque was recorded, and the torque curve was printed after the test was over.

To measure the variation of printing density and gloss with the thickness of ink film, ten copies of prints were made using a printability tester（IGT Testing Systems, Holland, Model IGT C-1）. A simple printability R-I tester（Akira Seisakusho, Japan, Model RI-2）was also used for printability examination. The density and gloss were mea-sured using a densitometer（Gretag Macbeth, Switzerland, Model D-196）and a gloss meter（BYK Gardener, U. K.）. To measure the setting time, the sample print was made on coated paper with the R-I tester, and the set-off was mea-sured in 3 second intervals on the same paper. To measure the drying time, a 37-μm-thick uniform coating was formed on glass plates, and the time was measured until the coating became fully dried in a 60℃ oven. The rub resis-tance was measured 20 times using a rub resistance tester（Prufbau GmbH, Germany）after printing the samples with the R-I tester. Acid value was measured by the titration of potassium hydroxide solution using a titrator（Mettler-Tole-do, U. S. A., Model DL22）. Color was measured with a col-orimeter（Hach Lange, U. K., Model LICO 150）. Softening point was measured with the ball and ring method. Toler-ance was measured with the continuous addition of solvent of n-heptane to resin until the solution became cloudy, and the ratio of solvent amount to resin was set as the toler-ance.

3 Results and DiscussionThe property variation of the formulated inks using dif-

ferent molecular weights of resin and various soy oil esters was examined to find the best performance ink. The print-ing density and gloss are the ultimate properties represent-ing ink performance, and the emulsification characteristic

Table 1　‌‌List of varnish formulation and cooking condition.

Component A-1 A-2 B CResin1

Soy oilSoy oil ester

Solvent2

Total

50 15 35－100

50 15 35－100

45 15 40－100

40 15－

45100

Cooking condition3

Formulation AFormulation BFormulation C

200℃ / 30 minUsing FAME(A-1) and FAEE(A-2)

Using FABEUsing hydrocarbon solvent

1 Rosin-modified phenolic resin : Mw 80,000, A.V. 15, High viscosity resin

2 Solvent : Mineral oil distillate, Boiling range 290～360℃, Aniline point 72℃

3 Varnish cooker : automatic cooker (Novocontrol GmbH, Germany, Model Themotronic Ⅱ)

Table 2　List of ink formulation.

Component A BVarnish

Pigment*CaCO3

Esters Solvent

Total

50151015－90

501510－2095

ConditionFormulation AFormulation B

Three roll mill/ 3 PassUsing vegetable esters

Using hydrocarbon solvent* Pigment: Phthalocyanine Beta Blue (CI Pigment Blue 15:3)

Solvent-free offset ink using vegetable oil esters

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and physical properties of ink are closely related to the ul-timate properties. The itemized assessment of the property variation from different raw materials for the ink formula-tion are addressed below.

3.1 Role of resin molecular weightThe properties of the rosin-modified phenolic resin used

in this experiment are listed in Table 3. The molecular weight increases from PM 15 to PM 88, of which the number is the molecular weight of the resin in thousands. The measurement result of the cloud point and tolerance showes that the solubility of PM 46 and 88 is lower than others. The acid value and color of the phenolic resins are unrelated to their molecular weight, whereas the softening point is raised with the molecular weight as in the previous study14）.

When the resin was converted to varnish and ink, its emulsification was affected more by its solubility than by its molecular weight, as shown in Fig. 1. The cooking con-dition of the sample is given as A-1 in Table 1 except the resin of different molecular weights used. The torque curves were obtained from the emulsification tester, while water was added as represented with the straight line. The water was supplied after 50 minutes from the beginning, and the steady increase indicated constant supply at a rate of 2 g/min. Initially the maximum torque was measured, when the spindle of the tester immersed in the static sample began to rotate. Then the torque reduced to a steady value, while the rotation settled. At the moment of water addition, the torque dropped until the water mixed with the sample completely. Then the torque increased steadily until the excess water was supplied, when the torque began to reduce. The curves in Fig. 1 show the same pattern of torque variation except the prolonged high torque during emulsification. The samples, PM 46 and PM 88, having low solubility required higher water pick-up for emulsification than others. The increased solubility reduces the surface activity of the resin molecules for emulsifica-tion, and increases the hydrophobic property of the ink leading to low water-pickup. This means that better com-

patibility of the resin maintains a stable ink-water balance on the printing press. Kazlauciunas15） showed that the compatibility of the ink components improved the ink sta-bility.

Figure 2 shows the changes in the elastic modulus and viscous modulus of inks with varying shear stress. As shown in the figure the peak values of the moduli do not significantly vary with different molecular weights, but the moduli of PM 15 have much larger than the others at low shear stress. When the molecular weight of the resin is low, the shear thickening（dilatancy）occurs at low shear

Table 3　List of resin properties.

Resin1 Mw A. V.2 C. P.3 Tolerance S. P.4 Color5 (G. N.)PM　15PM　28PM　46PM　54PM　88

1572428060464315402988765

14.520.815.115.515.0

9 748 728

5∞2

4.54.5

154164164160170

1215 7 911

1 PM number - Phenolic resin molecular weight in thousands.2 Acid value3 Cloud point (℃)4 Softening point (℃)5 Gardner number

Fig. 1　‌Torque curves of the varnishes(a) and inks(b) with different molecular weights of resin.

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stress16） and the pigment in ink with the resin is rearranged to become powder. The measured moduli of PM 15 indicate the shear thickening giving the high moduli. The changes in elastic and viscous moduli with the varying frequency of cone oscillation in the rheometer are illustrated in Fig. 3. As shown in the figure, the resulting moduli at low fre-quency are similar for various resin molecular weights. The moduli are different at high frequency for the different mo-lecular weights, but the difference is not related to the mo-lecular weight. Hoath et al.17） indicated that ink rheology was not significant under low shear rate, but it was impor-tant at high shear rate. The moduli spread at the high fre-quency cone oscillation shown in the figure are also yielded at the high shear rate in Fig. 3 somewhat less amount. However, there is no relation between the molecular weight of resin and the moduli at the motion of high fre-quency cone oscillation.

Figure 4 demonstrates the variations of printing density

and gloss according to the film thickness of ink for the printability analysis with the printability tester. The con-secutive 10 marks in each curve indicate the increasing number of printing from one to ten. The results show that high resin solubility gives high density and high gloss. Among the high solubility resins the larger molecular weight resin has slightly higher density. Note that PM 46 and PM 88 are of low solubility. From the viewpoint of ink mileage－ the ink weight transferred at the given number of printing copy－ the lower the resin solubility is, the less ink transfers due to the low amount solved. Therefore, it is expected that the resin having better solubility and larger molecular weight gives higher ink mileage. These resin properties in the offset ink indicate that the higher molecu-lar weight and better compatibility resin gives good print-ability and print quality as similar results found from the previous study8）.

The measurement results of printing density, gloss, setting time, and rub resistance using the R-I tester are listed in Table 4. It is noted that the density and gloss of

Fig. 2　‌Elastic and viscous modulus curves of inks with different molecular weights of resin at varing shear stress.

Fig. 3　‌Elastic and viscous modulus curves of inks with different molecular weights of resin at varing frequency of cone oscillation.

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PM 46 are low, of which the solubility is also low. For the other resins, the density and gloss generally improve as the molecular weight increases. In case of setting time, low sol-ubility gives fast setting as shown in PM 46 and PM 88, and for high solubility the high molecular weight leads to fast setting. The rub resistance generally becomes better as the resin molecular weight increases, which suggests that the ink film becomes strong when dried due to the high molec-ular weight of the resin.

3.2 Fatty acid estersTable 5 shows the kinematic viscosity, density and cloud

point of the vegetable esters and petroleum-based hydro-carbon solvent used in this study. The kinematic viscosity is relatively low for FAME and FAEE, whereas FABE and hydrocarbon solvent have high kinematic viscosity. The molecular weight of esters increases as alkyl chain becomes longer, and the kinetic viscosity also increases. While the density of solvents is similar, the cloud point of vegetable esters is much lower than that of hydrocarbon solvent, which implies that esters have good resin solubility.

Figure 5 shows the results of the emulsification analysis of varnish and ink processed with various esters and hy-drocarbon solvent. The cooking condition of the samples is given in Tables 1 and 2. The results suggest that the emul-sification of ink is affected by the resin dilution power in solvents. The cloud point of hydrocarbon solvent is much higher than esters as listed in Table 5, and the apparent difficulty of its emulsification is demonstrated in Fig. 5. Among the ester solvents the cloud point is similar, and the kinematic viscosity determines the emulsification. The lowest kinematic viscosity of FAME helps the emulsifica-tion the most, and the same result has been published by Lin and Lin18）. The variation of elastic and viscous moduli according to the shear stress of inks with different solvents is illustrated in Fig. 6. Among the ester solvents, the moduli differ at low shear stress, which suggests that the resistance to external force increases at the low shear stress due to the difficulty of emulsification indicated by the cloud point listed in Table 5. Therefore, pigment parti-cles are not evenly distributed at the low shear stress with high modulus ester. On the other hand, the hydrocarbon solvent maintained constant moduli from low to high shear stresses. This implies that the resistance to distortion in the entire shear stress ranges is equally high, and it is due to the low resin solubility for the hydrocarbon solvent rep-resented with high cloud point.

Figure 7 demonstrates the variation of elastic and viscous moduli for the varying frequency of cone oscillation for inks with different solvents. In this case, the hydrocar-bon solvent gives the highest moduli as seen in the figure, and it indicates that the ink preparation with high speed processing does not help with the hydrocarbon solvent. The variation of the printing density and gloss with differ-

Fig. 4　‌Printing density and gloss of inks with differ-ent molecular weights of resin at varing ink film thickness.

Table 4　‌‌Printing properties of inks with different molecular weights of resin.

PM 15 PM 28 PM 46 PM 54 PM 88Printing density

GlossSetting time (s)Rub resistance*

2.3454627

2.3057.5518

2.0755157

2.3357.7437

2.3658.5226

* Rub resistance ( 1.0 : Good ↔ 10.0 : Bad)

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ent thicknesses of ink film is plotted in Fig. 8. The consecu-tive 10 marks in each curve indicate the increasing number of printing from one to ten. The results show that the printing density and gloss of the ink with hydrocarbon solvent are much lower than those of ester inks. The low printing density explains that the ink transfer weight of the hydrocarbon ink is low from the start until higher number of printing. It is due to low resin content and solubility of the ink made of the solvent. Among the esters the ink of FAME has relatively low gloss, and it is because the low emulsification as shown in Fig. 6. The low emulsification makes the ink penetration into the surface of the substrate difficult and reduces the surface smoothness of printed

film of the ink. When the ink transfer weight represented with printing density was analyzed from the ink mileage, the variation of ink transfer weight of FABE was less than that of FAME when the printing number was increased as demonstrated in Fig. 8. This suggests that solvents in the ink play the role of vehicle affecting the ink transfer weight. In particular, FABE shows relatively small changes in the ink transfer weight and gloss with the increased number of printing, which is advantageous to the stability

Table 5　Properties of vegetable fatty acid esters.

　 FAME1 FAEE2 FABE3 H. S.4

Kinematic viscosity (40℃, cSt)Density (g/cm3)Cloud point (℃)

4.6790.8824

1

4.8400.8870－3

8.3000.8660－5

8.5370.8796

321 Fatty acid methyl ester2 Fatty acid ethyl ester3 Fatty acid butyl ester4 Hydrocarbon solvent

Fig. 5　‌Torque curves of the varnishes (a) and inks (b) with different solvents.

Fig. 6　‌Elastic and viscous modulus curves of inks with different solvents at varing shear stress.

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J. Oleo Sci. 62, (6) 345-352 (2013)

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of quality in printing process. The measurement results of printing density, gloss,

setting time, and rub resistance after printing of a sample copy using the R-I tester under the same condition are listed in Table 6. The density and gloss of the hydrocarbon solvent were lower than those of vegetable esters. The setting time was affected more by the kinematic viscosity than by the resin solubility of solvent, when the same resin was used. Regardless of the resin content and solubility, FAME and FAEE having lower kinematic viscosity show faster setting time. It suggests that the fast penetration of ink into the substrate surface immediately after printing has strong influence.

The rub resistance of vegetable esters is better than that of the hydrocarbon solvent, and it implies that the strength of ink film is affected by the high resin content of ink and the oxidation polymerization at the double bonds of vege-table esters. Among the vegetable esters, FAME shows lower rub resistance due to the low surface smoothness of ink film than FABE, and FAEE gives better rub resistance due to better printing density even if the kinematic viscosi-

ty of the solvent is lower. In a similar study6）, it was found that vegetable esters of good compatibility gave better printing density, gloss, and ink transfer than hydrocarbon solvent. Though the esters give similar printing properties of density, gloss and rub resistance, the smallest change of ink transfer weight upon multiple number of printing ob-tained from FABE improves the stability of ink quality the most.

4 CONCLUSIONSThe property variation of inks with varying molecular

weight of resin and different solvents of soy-oil fatty acid esters was investigated to find the best ink formulation. The comparison of print quality of various inks made of the different molecular weight of resin and fatty acid methyl ester（FAME）as solvent indicates that higher molecular weight and better solubility resin gives better printability

Fig. 7　‌Elastic and viscous modulus curves of inks with different solvents at varing frequency of cone oscillation.

Fig. 8　‌Printing density and gloss of inks with different solvents at varing ink film thickness.

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and print quality. The experimental results demonstrate that larger molecular weight resin having better solubility gives higher ink transfer leading to better ink performance.

The role of ester solvent was examined with the inks for-mulated with different esters and high molecular weight resin. The experimental comparison of print quality dem-onstrates that the fatty acid butyl ester（FABE）gives the best printing quality due to its high kinematic viscosity. The high viscosity leads to the smallest change of ink transfer weight upon multiple number of printing resulted in the high stability of ink quality.

ACKNOWLEDGMENTSFinancial support from the Dong-A University Research

Fund is gratefully acknowledged.

References1） Hong, Y. K.; Hong, W. H. Korean Chem. Eng. Res., 45,

424（2007）.2） Lee, K. W.; Hailan, C.; Yinhua, J.; Kim, Y. W.; Chung, K.

W. Korean J. Chem. Eng., 25, 474（2008）.3） Hong, W. P.; Park, J. Y.; Min, K.; Ko, M. J.; Park, K.;

Yoo, Y. J. Korean J. Chem. Eng., 28, 1908（2011）.4） Vogel, T. C. Proc. 45th Ann. Conf. Tech. Assoc.

Graphic Arts, Minneapolis, U.S.A.（1993）. 5） Pennaz, T. J. Proc. 46th Ann. Conf. Tech. Assoc.

Graphic Arts, Baltimore, U.S.A.（1994）. 6） Roy A. S.; Bhattachjee, M.; Mondal, R.; Ghosh, S. J.

Oleo Sci., 56, 623（2007）.7） Chou, S. M. Proc. 43rd Ann. Conf. Tech. Assoc.

Graphic Arts, N. Y., U.S.A.（1991）.8） Kim, S. B. J. Korean Print. Soc., 12, 145（1994）.9） Chou, S. M. Cher, M. Proc. 41st Ann. Conf. Tech. As-

soc. Graphic Arts, Orlando, U.S.A.（1989）.10） Cho, J. W.; Kim, S. B.; Park, J. M. J. Korean Print.

Soc., 20, 7（2002）.11） Park, J. M.; Kim, S. B.; Cho, J. W. J. Korean Print.

Soc., 21, 71（2003）.12） Kolon Chemical Co., Private Communication（2001）.13） Leach, R. H.; Armstrong, C.; Brown, J. F.; Mackenzie, M.

J.; Randall, L.; Smith, H. G. The Printing Ink Manual, 4th Ed., Van Nostrand Reinhold, N. Y., U.S.A.（1988）.

14） Xu, C.; Wang, S. S.; Shao, L.; Zhao, J. R.; Feng, Y. Polym. Adv. Tech., 23, 470（2012）.

15） Kazlauciunas, A. Color. Tech., 126, 315（2010）.16） Peng, K.; Zhu, J. G.; Feng, S. R.; Wang, R.; Liu, H. L. J.

Central South Univ., 19, 1988（2012）.17） Hoath, S. D.; Hutchings, I. M.; Martin, G. D.; Tuladhar,

T. R.; Mackley, M. R.; Vadillo, D. J. Imag. Sci. Tech., 53, 41208（2009）.

18） Lin, C. Y.; Lin, H. A. Fuel Process. Tech., 89, 1237（2008）.

Table 6　Printing properties of inks with differnt solvents.

　 FAME1 FAEE2 FABE3 H. S.4

Printing densityGloss

Setting time (s)Rub resistance5

2.4151.5186.0

2.4354.7234.5

2.4052.4285.0

2.2131.4278.5

1 Fatty acid methyl ester2 Fatty acid ethyl ester3 Fatty acid butyl ester4 Hydrocarbon solvent5 Rub resistance (1.0 : Good ↔ 10.0 : Bad)