The wettability effect of branched polyglycerols used as performance additives for water-based printing inks

The wettability effect of branched polyglycerols used as performance additives for water-based... J. Coat. Technol. Res., 15 (3) 649–655, 2018 https://doi.org/10.1007/s11998-018-0055-6 BR IEF C OM MUNICATI ON The wettability effect of branched polyglycerols used as performance additives for water-based printing inks Mariusz Tryznowski, Zuzanna Zołek-Tryznowska, Joanna Izdebska-Podsiadły The Author(s) 2018. This article is an open access publication Abstract The aim of this work was to study the Introduction influence of primary and secondary hydroxyl groups in the branched polyglycerol on the selected properties of Hyperbranched polymers (HBPs) and dendrimers are water-based printing ink and copies printed with water- a new class of polymers. Dendrimers are characterized based flexographic printing inks. The branched polyg- by a highly branched structure of great regularity and a lycerols were synthesized through anionic ring-opening compact shape, with a large number of polar end polymerization using trimethylolpropane as a starting groups and symmetry in structure. Hyperbranched material. Obtained polyglycerol exhibited an irregular polymers are globular and highly branched macro- structure containing primary and secondary or pre- molecules with a large number of functional groups. In dominantly primary hydroxyl groups in the macro- contrast, HBPs exhibit polydispersity and irregularity 1 13 molecule. The analysis (FTIR, H NMR, CNMR) in terms of branching and structure. confirmed the structure of polyglycerols. Obtained Dendrimers and hyperbranched polymers have polyglycerols were then used as a performance additive found a number of applications in the printing industry. in a water-based flexographic printing ink. The contact HBPs polymers may be used in the printing industry as angles of the printing inks on the printing base were performance additives for offset or flexographic print- measured. The impact of a small amount of branched ing inks in order to improve print quality and print polyglycerol on the printing ink color was examined by performance, for instant gloss of the print, adhesion of studying the optical density of a full-tone area, the the dried ink film to the printing substrate, and 2–4 color values (CIELAB), the total color difference abrasion resistance of print. Dendrimers and hyper- DE , and gloss of the dried ink film. In general, the branched polymers characterized by regular structure ab addition of branched polyglycerol containing only have found application in printing inks, wherein a dye primary hydroxyl groups improved the wettability of or pigment is incorporated in the dendrimer molecule the plastic film and gloss of printing ink with an of the printing ink dedicated for ink-jet printing 5–7 acceptable total color difference DE in contrast to technology. Furthermore, commercially available ab branched polyglycerol with primary and secondary dendrimers PAMAM (Dendritech, USA) are used hydroxyl groups. in ink-jet inks dedicated for printing on various nonabsorbent and nonporous surfaces (glass, metal, Keywords Polyglycerol, Flexographic water-based plastic bases) characterized by improved water and 8,9 inks, Performance additives, Wettability moisture and deteriorated abrasion resistance. In addition, hyperbranched polycarbonates can be used as pigment dispersants in offset and flexographic printing inks, dyeing fibers paints, or wall and fac ¸ ade paints. Last but not least, hyperbranched polyesters were used in order to modify the properties of flexographic solvent-based printing inks. The addition of hyper- TM M. Tryznowski (&), Z. Zołek-Tryznowska, branched polyesters from Boltorn family improved J. Izdebska-Podsiadły the color properties of the overprinted sample and its Faculty of Production Engineering, Warsaw University of 11,12 abrasion resistance. Technology, Narbutta 85, 02-524 Warsaw, Poland e-mail: m.tryznowski@wip.pw.edu.pl 649 J. Coat. Technol. Res., 15 (3) 649–655, 2018 Flexographic printing technology requires low and Materials and methods rapid viscosity inks. The viscosity should be lower than 0.05–0.5 PaÆs. However, this technology is Materials suitable for printing on paper materials, as well as nonporous and nonabsorbent substrates used in All of the reagents for polyglycerol synthesis were packaging industry. There are three types of flexo- ´ purchased from Sigma-Aldrich (Poznan, Poland) and graphic inks used for these applications: water-based, were used as received, without further purification. solvent-based, and UV curable. Nowadays, due to As an original printing ink, water-based printing ink ecological reasons, attention in the printing industry is (FlexiWet), color black, supplied by Chespa (Poland) focused on production of water-based printing inks in was used. This ink was characterized with a kinematic order to minimize the evaporation of organic solvents viscosity of 19 s. This printing ink is recommended for into the environment. Printing with water-based inks printing on plastic films. For printing, oriented on nonabsorbent substrates, for instance, plastic films, polypropylene (BOPP), polyethylene (PE), and is linked with some problems. The adhesion of the polyethylene terephthalate films were used. The water-based ink film to the plastic film is worse than plastic films were activated by a corona treatment, solvent-based ink because of a low proper wetting of and they were transparent and had a thickness of these surfaces. Moreover, the wet rub resistance of 20 lm for BOPP, 50 lm for PE, and 12 lm for PET. overprinted plastic films with water-based inks is usually poor. It is well known that the surface tension of flexographic printing ink has to be lower than the Characterization of polyglycerol surface free energy of the plastic film to allow proper wetting and adhesion between the layers of the ink The chemical structure of obtained polyglycerols was film and the plastic film. In order to decrease the characterized on a Bio-Rad FTS 165 FTIR spectrom- 1 13 surface tension of water-based inks, organic co- eter using KBr pellets. Hand C NMR spectra were solvents or surfactants are added into water-based recorded at room temperature, using tetramethylsilane inks. as an internal standard and deuterated solvent In our work, we propose addition of branched (DMSO-d ), on a Varian VXR 400 MHz spectrometer; oligo- and polyglycerols into water-based printing the spectra were analyzed using MestReNova v.6,2,0- inks instead of surfactants or volatile co-solvents. 7238 (Mestrelab Research S.L) software. Polyglycerols are environmentally friendly, biodegradable, biocompatible, and nontoxic. Further- more, oligoglycerols (2–10 units) are approved as Synthesis of polyglycerol food and pharma additives by the FDA ; therefore, hyperbranched polyglycerols have already found Synthesis of PG-1 15,16 application in drug delivery systems. Tradition- ally, oligo- and polyglycerols are used in different Potassium (0.97 g, 0.025 mol) was placed together with industries, i.e., food, pharmaceutical, cosmetic, soap, trimethylolpropane (10.0 g, 0.075 mol) in a 500-mL 17,18 toothpastes, fuel, or paint. Hyperbranched polyg- round flask equipped with a magnetic stirrer and a lycerol has already found applications as surfactants thermometer. Then the mixture was heated at elevated in liquids for treating lithographic printing plates or temperature (65C) at inert gas atmosphere for 15 min. as an organic solvent in a water-based ink-jet printing Next, a mixture of ethoxyethyl glycidyl ether, EEGE 20,21 ink in order to prevent paper deformation. (131.56 g, 0.9 mol), dissolved in THF was added at a Polyglycerols are much more stable against acidic rate of 1.5 mL h to the mixture using a dosing pump or basic hydrolysis in contrast to polyesters. Fur- at elevated temperature (95C). Simultaneously, the thermore, the advantage of polyglycerols is their THF was removed from the reaction mixture. Upon remarkable solubility in water due to the functional the completion of adding the EEGE, methanol (150 g) hydroxyl end groups. and 15% hydrochloric acid (150 g) were added to the The aim of this work is to present a wettability effect reaction mixture. The reaction mixture was stirred for of branched polyglycerols containing predominantly 24 h at 50C. Next, the reaction mixture was neutral- primary hydroxyl groups or primary and secondary ized by adding solid potassium carbonate, and the hydroxyl end groups and the possibility of their solvent was removed under reduced pressure applications on the printing ink and print properties. (0.5 mmHg). The obtained product was a dark yellow, The structures of obtained polyglycerols are presented viscous liquid. in Fig. 1. The influence of polyglycerol on several Yield 123.1 g (87%), H NMR (DMSO-d , printing ink properties (rheology, contact angle) and 500 MHz); d (ppm) = 4.75–4.50 (m, 15H, OH), 3.67– print quality parameters (optical density, color values, 3.14 (m, 64H, CH O, CHO and CH O ), 1.33–1.19 2 2 TMP and gloss) was estimated. (m, 2H, CH O ), 0.83–0.71 (m, 3H, CH ); C 2 TMP 3TMP 650 J. Coat. Technol. Res., 15 (3) 649–655, 2018 HO HO O H OH OH PG-1 OH OH HO OH HO OH HO OH HO HO OH OH OH OH PG-1,2 Fig. 1: Structures of obtained polyglycerols NMR (DMSO-d , 125 MHz); d (ppm) = 80.0, 70.4 , (0.5 mmHg). The obtained product was a light yellow, 6 TMP 69.4, 60,9, 64.6, 60.1, 42.8 , 22.6 ; FTIR (KBr): m viscous liquid. TMP TMP 1 1 (cm ) = 803, 839, 1040, 1105, 1202, 1457, 2281, 2934, Yield 126.8 g (89%), H NMR (DMSO-d , 3292. 500 MHz); d (ppm) = 4.78–4.49 (m, 13H, OH), 3.65– 3.11 (m, 61H, CH O, CHO and CH O ), 1.34–1.1 2 2 TMP (m, 2H, CH O ), 0.84–0.70 (m, 3H, CH ); C 2 TMP 3TMP Synthesis of PG-1,2 NMR (DMSO-d , 125 MHz); d (ppm) = 80.0– 79.0 , 71.8–70.4 , 69.5–69.1 , 60.7– CH2O TMP CHOH Potassium (0.97 g, 0.025 mol) was placed together with 61.1 , 42.8 , 22.6 ; FTIR (KBr): m (cm )= CH2OH TMP TMP trimethylolpropane (10.0 g, 0.075 mol) in a 500-mL 804, 839, 1041, 1101, 1200, 1457, 2280, 2931, 3300. round flask equipped with a magnetic stirrer and a thermometer. Then the mixture was heated at elevated temperature (65C) at inert gas atmosphere for 15 min. Preparation and characterization of inks Next, a mixture of glycidol (66.67 g, 0.9 mol) dissolved in THF was added at a rate of 1.5 mL h to the The modified ink was prepared by drop-wise addition mixture using a dosing pump at elevated temperature of a calculated weight of polyglycerol to pure FlexiWet (95C). Next, after 33 h of adding the mixture of ink, while continuously stirring. The mass fraction of glycidol with ether, the obtained product was dissolved LPG was 0.01, because the best print quality was in water and neutralized by 10% hydrochloric acid. obtained after addition of 0.01 of the hyperbranched 11,12 The solvent was removed under reduced pressure polyglycerols. Then the ink was stirred for 30 min using a mechanical stirrer. The rheological character- 651 J. Coat. Technol. Res., 15 (3) 649–655, 2018 istics of the printing inks (the original process printing direction according to ISO standard, and the reported ink and the ink with added hyperbranched polyglyc- values are the average of these measurements. erol) were specified by the flow time in a flow cup (volume 100 mL, outlet diameter 4 mm), according to an ISO standard. The measurements were taken at Results and discussion 23C; the relative error in the measurements was less than 3%, and the kinematic viscosity was 19 ± 0.5 s for Polymer synthesis and characterization the printing inks. Contact angle and surface tension measurements of the investigated inks were taken In this work two branched polyglycerols were synthe- using a DSA 30E drop shape analysis system (Kru ¨ ss, sized in order to assess the wettability and hydroxyl Germany). Smooth and horizontal sessile drops of the group effect. Obtained polymers were synthesized liquids were deposited on a solid surface plastic film through a ring-opening polymerization using TMP as (BOPP, PE, PET) using needles of 0.5 mm diameter. a starting material (see Fig. 1). Branched polyglycerols The contact angle was measured on static drops. The were characterized by irregular branched structure and drop shape analysis was done 15 s after the drop predominately with primary hydroxyl functional deposition with Tangent method 1. The surface tension groups (PG-1) or with secondary and primary hydroxyl of investigated inks was determined by pendant drop groups (PG-1,2). Our previous work shows that method using needles of 2 mm diameter. Environmen- branched glycerols have a positive effect on the tal conditions were stable, with temperature 23 ± 1C. wettability, the adhesion, and wet or dry rub resis- The reported contact angle and surface tension values 18,26,27 tance. are the mean of five samples. Ink properties Printing and characterization of prints Before printing, the selected properties of the printing Laboratory printing was carried out with a Flexiproof ink were estimated: the wettability of the printing base instrument (TMI Machines, UK). The printing speed by the ink (by measuring the contact angle of printing was 60 mÆmin , and the printing engagement was 38, ink on the various plastic films) and surface tension 31, and 26 for PET, BOPP, and PE plastic films, (pendant drop method). respectively. The printing plate, made of a photopoly- The printability of polymer bases depends on mer prepared by the digital laser photochemical wettability of the bases by the printing ink. Further- method, had dimensions of 260 9 90 mm and a thick- more, the wettability of the base by the inks influences ness of 1.7 mm. The pressure between the anilox the adhesion between the base and the dried ink layer, 3 2 engraved roller (6 cm Æm volume, resolution or line the print quality, and mechanical properties of prints. ruling of 160 lines per cm ) and the plate cylinder was 98. All factors were kept constant during the printing process (printing speed, anilox roller, and printing 70 33 pressure). Printing was performed under controlled 64.7 environmental conditions of 23C and 50% relative 58.0 humidity (RH). 52.4 The optical densities of full-tone area, 75% tone 32.0 fields, L*, a*, b* measurements, and gloss of prints 11,12 were precisely described in previous works. The 37.7 optical densities of the full-tone area and specific ink 34.5 color components L*, a*, b* were determined using a 31.8 31 30.7 29.5 SpectroEye spectrophotometer (GretagMacbeth, 30 27.1 Switzerland). Measurements of the optical density of the full-tone area were taken at the following settings: 30.2 D50 illuminant using a 2 observer, 0/45 measuring 29.9 geometry, with a polarization filter, white standard: proofing paper. The measurements of L*, a*, b* were taken using these settings with absolute as a white 0 29 standard according to ISO standard. The reported FlexiWet FlexiWet + 1% PG-1,2 FlexiWet + 1% PG-1 results are the average of the measurements from a Prinng ink minimum of six areas on two different prints. BOPP PE PET Surface The gloss (in the gloss units, GU) of the prints was measured at 20,60, and 85 geometry conditions with Fig. 2: Properties of investigated printing inks: contact the use of a Picogloss (BYK-Gardner, Germany). Data angle and surface tension measured at t =23C for the original flexographic printing ink and after the addition of collection was performed at six different positions of polyglycerols the samples in both directions: cross and machine Contact angle (°) Surface tension (mN/m) J. Coat. Technol. Res., 15 (3) 649–655, 2018 5 70 Better wettability (so smaller values of contact angles) should indicate better adhesion of the ink layer to the base. The wettability may be estimated as a direct measurement of the static contact angle of the ink on the base. The contact angle together with surface tension of the ink without and with the addition of 2.72 investigated polyglycerols is shown in Fig. 2. The 2.67 2.58 addition of PG-1 decreases the contact angle of the 2.33 ink; therefore, an improvement of the wettability is 2.02 1.98 1.82 1.71 1.69 observed. The addition of PG-1 decreases the contact angle from 29.5 to 27.1.4, from 58.0 to 52.4, and from 34.5 to 30.7, for the BOPP, PE, and PET plastic film, respectively. In general, the addition of PG-1 decreases the contact angle about 9–12%. On the other hand, the addition of PG-1,2 increases the 0 30 contact angle of the ink. The higher contact angles FlexiWet FlexiWet + 1% PG-1,2 FlexiWet + 1% PG-1 are observed for the PE plastic film, and the lower Prinng ink contact angles for the BOPP plastic film. BoPP PE PET Gloss BoPP Gloss PE Gloss PET The surface tension of the ink slightly increases with an increasing mass fraction of polyglycerols. The Fig. 3: Optical densities of full-tone area and gloss of ink highest value of surface tension was observed for the layers printed with the investigated printing inks printing ink containing PG-1 (32.0 mNÆm ), which is higher than surface tension of solvent-based inks we 11,12 ink layers. It is well known that the thickness of the previously observed. Hence, the values of surface dried ink layer depends on the wettability of the base tension are higher than the surface free energy of by the ink during the printing process. Better wetta- typical plastic films, i.e., the surface free energy of bility is connected with a thinner dried ink layer and untreated PE and BOPP is lower than 30 mJÆm ,as lower optical density, assuming constant division of the reported in the literature. The printing process ink in the inking unit during the printing process, not requires that the surface tension of the printing ink is influenced by the used additive. The optical density of lower than the surface free energy of the plastic film. full-tone area decreases with the addition of the PG-1. On the other hand, values of optical density of prints overprinted with the ink with the addition of PG-1,2 Print quality are higher than for originally printing ink or ink with the addition of PG-1. However, it should be mentioned The print quality was determined as the properties of that all optical density values are high. The flow curves the print, i.e., the optical density of the full-tone area, of printing inks were presented by us previously ; the the optical density of 75% tone fields, the color values presence of polyglycerols had a noticeable effect on the (L*, a*, b*), and gloss. flow curve. This effect is strongly related to contact Before print quality measurements are taken, the angle of the printing ink on the printing base. It might adhesion of the dried ink film should be quantified by 30,31 be connected with the greater capacity of primary simple adhesion test (tape test). Adhesion of the hydroxyl groups in the macromolecule for hydrogen original ink to BOPP and PE base was generally much bonding. The incorporation of secondary hydroxyl better than adhesion on a PET film. The adhesion of groups into the branched molecule of polyglycerol the dried ink film modified with obtained polyglycerol unfavorably affects the wettability effect of the printing was noticeably better. However, the values of contact ink, and the contact angle is higher together with angles on the plastic films indicate that the better optical density of full-tone area and gloss. adhesion to the BOPP or PET than to PE film is Gloss is one of the most important parameters in expected. Probably, the interaction between the dried printing and packaging technology, because gloss ink film and the top layer of PET film is quite poor. affects the print quality by providing a better overall The indirect method of assessing adhesion may be the look and greater depth to colors. Gloss is a property measurements of abrasion resistance. The dry and wet of a material that is responsible for light reflection from abrasion resistance of overprinted PE, BOPP, and PET a surface. The methods for measuring gloss depend on base by printing ink containing PG-1,2 is visibly worse the kind of base that is used. The original FlexiWet than prints overprinted with original printing ink or printing ink is a middle–high gloss, so the gloss values printing ink with the addition of PG-1. were in the range 30–70 gloss units (GU). Hence, a The values of optical density of full-tone area, measuring geometry with an angle of 60 was used optical density of 75% tone fields, relative printing according to the ISO standard. In general, the contrast, and gloss are listed in Fig. 3. The optical addition of polyglycerols to the FlexiWet printing ink density assesses the thickness of the dried ink layer. increases the gloss of the prints. This effect is stronger Higher values of optical density refer to thicker dried Opcal density Gloss J. Coat. Technol. Res., 15 (3) 649–655, 2018 Table 1: L*, a*, b* values and total color difference DE of ink layers printed with the investigated printing inks ab Printing ink L* a* b* DE ab BOPP FlexiWet 2.58 0.77 0.87 FlexiWet + 1% PG-1,2 1.44  0.03  0.46 1.9 FlexiWet + 1% PG-1 5.97 2.04 3.26 4.3 PE FlexiWet 9.70 0.33 0.50 FlexiWet + 1% PG-1,2 19.36  0.19  0.29 9.7 FlexiWet + 1% PG-1 5.04 1.56 2.38 5.2 PET FlexiWet 2.01 0.32 0.27 FlexiWet + 1% PG-1,2 1.62  0.04  0.19 0.7 FlexiWet + 1% PG-1 6.87 2.11 3.63 6.2 for the PG-1 than for PG-1,2. The differences are in the Obtained polyglycerols PG-1,2 and PG-1 exhibited range of 12.1 GU for BOPP prints, 5.1 GU for PE irregular structure containing primary and secondary prints, and 7.2 for PET prints for the printing ink hydroxyl groups or predominantly primary hydroxyl containing PG-1. The gloss of the prints is also related groups in the macromolecule, respectively. Polyglyc- to better wettability of the printing ink and smoothing erols were synthesized by ring-opening polymerization process of the printing ink while drying. using trimethylolpropane as a starting material. The color values (L*, a*, b*) together total color The impact of the polyglycerols on the wettability, differences are presented in Table 1. The total color surface tension, optical density, and color parameters differences (DE ) were calculated from equation : (L*, a*, b*) is reported in this paper. The addition of ab branched polyglycerols strongly affects the wettability qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi of the base by printing ink. Furthermore, the wettabil- 2 2 DE ¼ ðDL ÞþðDa Þ þðDb Þ ab ity of the ink on the film influences the print quality. We have proven that polyglycerols containing pre- where DL*, Da*, and Db* are the differences between dominately primary hydroxyl groups in the macro- the value of the ink with the addition of polyglycerols molecule have improved the print quality of the prints. and the original ink. The L* value is a measure of the Our results help to understand phenomena which lightness of an object and is quantified on a scale where occur during printing, support the use of branched L* = 0 for a perfect black diffuser and L* = 100 for a polyglycerols as performance additives for water-based perfect reflecting diffuser. For BOPP and PET printing printing inks, and may open up new possibilities for bases, the values of L* decrease with the addition of applications of these environmentally friendly poly- PG-1,2 and increase with the addition of PG-1. This mers. effect is strongly connected with optical density and the thickness of the dried printing ink. The thinner layer of Acknowledgments Funding for this research was printing ink is related to the ‘‘lighter color’’ of the ink. provided by National Science Centre of Poland based Therefore, low values of total color difference (DE ) on decision nr DEC-2013/11/D/ST8/03371. ab are observed for the printing ink with the addition of PG-1,2; the values are lower than 2, demonstrating that differences occurred but it cannot be observed with the Compliance with ethical standards human naked eye. Furthermore, higher values of DE ab are observed for the printing ink with the addition of Conflict of interest The authors declare that there is PG-1, due to the thinner printing ink layer. The no conflict of interests regarding the publication of this overprinted PE base was characterized by very poor paper. print quality, and the values of color values (L*, a*, b*) and total color differences are quite high. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/li censes/by/4.0/), which permits unrestricted use, distri Conclusions bution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and In this work, we have demonstrated the wettability the source, provide a link to the Creative Commons effect of branched polyglycerols and the impact of license, and indicate if changes were made. primary and secondary hydroxyl groups on wettability. 654 J. Coat. Technol. Res., 15 (3) 649–655, 2018 18. Zolek-Tryznowska, Z, Tryznowski, M, Izdebska, J, ‘‘Diglyc- References erol as an Environmentally Friendly Performance Additive for Water-Based Flexographic Printing Inks.’’ Przemysl 1. Seiler, M, ‘‘Hyperbranched Polymers: Phase Behavior and Chemiczny, 93 (11) 1970–1973 (2014) New Applications in the Field of Chemical Engineering.’’ 19. 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The wettability effect of branched polyglycerols used as performance additives for water-based printing inks

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/lp/springer_journal/the-wettability-effect-of-branched-polyglycerols-used-as-performance-x49WsJBH6S
Publisher
Springer Journals
Copyright
Copyright © 2018 by The Author(s)
Subject
Materials Science; Tribology, Corrosion and Coatings; Surfaces and Interfaces, Thin Films; Polymer Sciences; Industrial Chemistry/Chemical Engineering; Materials Science, general
ISSN
1547-0091
eISSN
1935-3804
D.O.I.
10.1007/s11998-018-0055-6
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Abstract

J. Coat. Technol. Res., 15 (3) 649–655, 2018 https://doi.org/10.1007/s11998-018-0055-6 BR IEF C OM MUNICATI ON The wettability effect of branched polyglycerols used as performance additives for water-based printing inks Mariusz Tryznowski, Zuzanna Zołek-Tryznowska, Joanna Izdebska-Podsiadły The Author(s) 2018. This article is an open access publication Abstract The aim of this work was to study the Introduction influence of primary and secondary hydroxyl groups in the branched polyglycerol on the selected properties of Hyperbranched polymers (HBPs) and dendrimers are water-based printing ink and copies printed with water- a new class of polymers. Dendrimers are characterized based flexographic printing inks. The branched polyg- by a highly branched structure of great regularity and a lycerols were synthesized through anionic ring-opening compact shape, with a large number of polar end polymerization using trimethylolpropane as a starting groups and symmetry in structure. Hyperbranched material. Obtained polyglycerol exhibited an irregular polymers are globular and highly branched macro- structure containing primary and secondary or pre- molecules with a large number of functional groups. In dominantly primary hydroxyl groups in the macro- contrast, HBPs exhibit polydispersity and irregularity 1 13 molecule. The analysis (FTIR, H NMR, CNMR) in terms of branching and structure. confirmed the structure of polyglycerols. Obtained Dendrimers and hyperbranched polymers have polyglycerols were then used as a performance additive found a number of applications in the printing industry. in a water-based flexographic printing ink. The contact HBPs polymers may be used in the printing industry as angles of the printing inks on the printing base were performance additives for offset or flexographic print- measured. The impact of a small amount of branched ing inks in order to improve print quality and print polyglycerol on the printing ink color was examined by performance, for instant gloss of the print, adhesion of studying the optical density of a full-tone area, the the dried ink film to the printing substrate, and 2–4 color values (CIELAB), the total color difference abrasion resistance of print. Dendrimers and hyper- DE , and gloss of the dried ink film. In general, the branched polymers characterized by regular structure ab addition of branched polyglycerol containing only have found application in printing inks, wherein a dye primary hydroxyl groups improved the wettability of or pigment is incorporated in the dendrimer molecule the plastic film and gloss of printing ink with an of the printing ink dedicated for ink-jet printing 5–7 acceptable total color difference DE in contrast to technology. Furthermore, commercially available ab branched polyglycerol with primary and secondary dendrimers PAMAM (Dendritech, USA) are used hydroxyl groups. in ink-jet inks dedicated for printing on various nonabsorbent and nonporous surfaces (glass, metal, Keywords Polyglycerol, Flexographic water-based plastic bases) characterized by improved water and 8,9 inks, Performance additives, Wettability moisture and deteriorated abrasion resistance. In addition, hyperbranched polycarbonates can be used as pigment dispersants in offset and flexographic printing inks, dyeing fibers paints, or wall and fac ¸ ade paints. Last but not least, hyperbranched polyesters were used in order to modify the properties of flexographic solvent-based printing inks. The addition of hyper- TM M. Tryznowski (&), Z. Zołek-Tryznowska, branched polyesters from Boltorn family improved J. Izdebska-Podsiadły the color properties of the overprinted sample and its Faculty of Production Engineering, Warsaw University of 11,12 abrasion resistance. Technology, Narbutta 85, 02-524 Warsaw, Poland e-mail: m.tryznowski@wip.pw.edu.pl 649 J. Coat. Technol. Res., 15 (3) 649–655, 2018 Flexographic printing technology requires low and Materials and methods rapid viscosity inks. The viscosity should be lower than 0.05–0.5 PaÆs. However, this technology is Materials suitable for printing on paper materials, as well as nonporous and nonabsorbent substrates used in All of the reagents for polyglycerol synthesis were packaging industry. There are three types of flexo- ´ purchased from Sigma-Aldrich (Poznan, Poland) and graphic inks used for these applications: water-based, were used as received, without further purification. solvent-based, and UV curable. Nowadays, due to As an original printing ink, water-based printing ink ecological reasons, attention in the printing industry is (FlexiWet), color black, supplied by Chespa (Poland) focused on production of water-based printing inks in was used. This ink was characterized with a kinematic order to minimize the evaporation of organic solvents viscosity of 19 s. This printing ink is recommended for into the environment. Printing with water-based inks printing on plastic films. For printing, oriented on nonabsorbent substrates, for instance, plastic films, polypropylene (BOPP), polyethylene (PE), and is linked with some problems. The adhesion of the polyethylene terephthalate films were used. The water-based ink film to the plastic film is worse than plastic films were activated by a corona treatment, solvent-based ink because of a low proper wetting of and they were transparent and had a thickness of these surfaces. Moreover, the wet rub resistance of 20 lm for BOPP, 50 lm for PE, and 12 lm for PET. overprinted plastic films with water-based inks is usually poor. It is well known that the surface tension of flexographic printing ink has to be lower than the Characterization of polyglycerol surface free energy of the plastic film to allow proper wetting and adhesion between the layers of the ink The chemical structure of obtained polyglycerols was film and the plastic film. In order to decrease the characterized on a Bio-Rad FTS 165 FTIR spectrom- 1 13 surface tension of water-based inks, organic co- eter using KBr pellets. Hand C NMR spectra were solvents or surfactants are added into water-based recorded at room temperature, using tetramethylsilane inks. as an internal standard and deuterated solvent In our work, we propose addition of branched (DMSO-d ), on a Varian VXR 400 MHz spectrometer; oligo- and polyglycerols into water-based printing the spectra were analyzed using MestReNova v.6,2,0- inks instead of surfactants or volatile co-solvents. 7238 (Mestrelab Research S.L) software. Polyglycerols are environmentally friendly, biodegradable, biocompatible, and nontoxic. Further- more, oligoglycerols (2–10 units) are approved as Synthesis of polyglycerol food and pharma additives by the FDA ; therefore, hyperbranched polyglycerols have already found Synthesis of PG-1 15,16 application in drug delivery systems. Tradition- ally, oligo- and polyglycerols are used in different Potassium (0.97 g, 0.025 mol) was placed together with industries, i.e., food, pharmaceutical, cosmetic, soap, trimethylolpropane (10.0 g, 0.075 mol) in a 500-mL 17,18 toothpastes, fuel, or paint. Hyperbranched polyg- round flask equipped with a magnetic stirrer and a lycerol has already found applications as surfactants thermometer. Then the mixture was heated at elevated in liquids for treating lithographic printing plates or temperature (65C) at inert gas atmosphere for 15 min. as an organic solvent in a water-based ink-jet printing Next, a mixture of ethoxyethyl glycidyl ether, EEGE 20,21 ink in order to prevent paper deformation. (131.56 g, 0.9 mol), dissolved in THF was added at a Polyglycerols are much more stable against acidic rate of 1.5 mL h to the mixture using a dosing pump or basic hydrolysis in contrast to polyesters. Fur- at elevated temperature (95C). Simultaneously, the thermore, the advantage of polyglycerols is their THF was removed from the reaction mixture. Upon remarkable solubility in water due to the functional the completion of adding the EEGE, methanol (150 g) hydroxyl end groups. and 15% hydrochloric acid (150 g) were added to the The aim of this work is to present a wettability effect reaction mixture. The reaction mixture was stirred for of branched polyglycerols containing predominantly 24 h at 50C. Next, the reaction mixture was neutral- primary hydroxyl groups or primary and secondary ized by adding solid potassium carbonate, and the hydroxyl end groups and the possibility of their solvent was removed under reduced pressure applications on the printing ink and print properties. (0.5 mmHg). The obtained product was a dark yellow, The structures of obtained polyglycerols are presented viscous liquid. in Fig. 1. The influence of polyglycerol on several Yield 123.1 g (87%), H NMR (DMSO-d , printing ink properties (rheology, contact angle) and 500 MHz); d (ppm) = 4.75–4.50 (m, 15H, OH), 3.67– print quality parameters (optical density, color values, 3.14 (m, 64H, CH O, CHO and CH O ), 1.33–1.19 2 2 TMP and gloss) was estimated. (m, 2H, CH O ), 0.83–0.71 (m, 3H, CH ); C 2 TMP 3TMP 650 J. Coat. Technol. Res., 15 (3) 649–655, 2018 HO HO O H OH OH PG-1 OH OH HO OH HO OH HO OH HO HO OH OH OH OH PG-1,2 Fig. 1: Structures of obtained polyglycerols NMR (DMSO-d , 125 MHz); d (ppm) = 80.0, 70.4 , (0.5 mmHg). The obtained product was a light yellow, 6 TMP 69.4, 60,9, 64.6, 60.1, 42.8 , 22.6 ; FTIR (KBr): m viscous liquid. TMP TMP 1 1 (cm ) = 803, 839, 1040, 1105, 1202, 1457, 2281, 2934, Yield 126.8 g (89%), H NMR (DMSO-d , 3292. 500 MHz); d (ppm) = 4.78–4.49 (m, 13H, OH), 3.65– 3.11 (m, 61H, CH O, CHO and CH O ), 1.34–1.1 2 2 TMP (m, 2H, CH O ), 0.84–0.70 (m, 3H, CH ); C 2 TMP 3TMP Synthesis of PG-1,2 NMR (DMSO-d , 125 MHz); d (ppm) = 80.0– 79.0 , 71.8–70.4 , 69.5–69.1 , 60.7– CH2O TMP CHOH Potassium (0.97 g, 0.025 mol) was placed together with 61.1 , 42.8 , 22.6 ; FTIR (KBr): m (cm )= CH2OH TMP TMP trimethylolpropane (10.0 g, 0.075 mol) in a 500-mL 804, 839, 1041, 1101, 1200, 1457, 2280, 2931, 3300. round flask equipped with a magnetic stirrer and a thermometer. Then the mixture was heated at elevated temperature (65C) at inert gas atmosphere for 15 min. Preparation and characterization of inks Next, a mixture of glycidol (66.67 g, 0.9 mol) dissolved in THF was added at a rate of 1.5 mL h to the The modified ink was prepared by drop-wise addition mixture using a dosing pump at elevated temperature of a calculated weight of polyglycerol to pure FlexiWet (95C). Next, after 33 h of adding the mixture of ink, while continuously stirring. The mass fraction of glycidol with ether, the obtained product was dissolved LPG was 0.01, because the best print quality was in water and neutralized by 10% hydrochloric acid. obtained after addition of 0.01 of the hyperbranched 11,12 The solvent was removed under reduced pressure polyglycerols. Then the ink was stirred for 30 min using a mechanical stirrer. The rheological character- 651 J. Coat. Technol. Res., 15 (3) 649–655, 2018 istics of the printing inks (the original process printing direction according to ISO standard, and the reported ink and the ink with added hyperbranched polyglyc- values are the average of these measurements. erol) were specified by the flow time in a flow cup (volume 100 mL, outlet diameter 4 mm), according to an ISO standard. The measurements were taken at Results and discussion 23C; the relative error in the measurements was less than 3%, and the kinematic viscosity was 19 ± 0.5 s for Polymer synthesis and characterization the printing inks. Contact angle and surface tension measurements of the investigated inks were taken In this work two branched polyglycerols were synthe- using a DSA 30E drop shape analysis system (Kru ¨ ss, sized in order to assess the wettability and hydroxyl Germany). Smooth and horizontal sessile drops of the group effect. Obtained polymers were synthesized liquids were deposited on a solid surface plastic film through a ring-opening polymerization using TMP as (BOPP, PE, PET) using needles of 0.5 mm diameter. a starting material (see Fig. 1). Branched polyglycerols The contact angle was measured on static drops. The were characterized by irregular branched structure and drop shape analysis was done 15 s after the drop predominately with primary hydroxyl functional deposition with Tangent method 1. The surface tension groups (PG-1) or with secondary and primary hydroxyl of investigated inks was determined by pendant drop groups (PG-1,2). Our previous work shows that method using needles of 2 mm diameter. Environmen- branched glycerols have a positive effect on the tal conditions were stable, with temperature 23 ± 1C. wettability, the adhesion, and wet or dry rub resis- The reported contact angle and surface tension values 18,26,27 tance. are the mean of five samples. Ink properties Printing and characterization of prints Before printing, the selected properties of the printing Laboratory printing was carried out with a Flexiproof ink were estimated: the wettability of the printing base instrument (TMI Machines, UK). The printing speed by the ink (by measuring the contact angle of printing was 60 mÆmin , and the printing engagement was 38, ink on the various plastic films) and surface tension 31, and 26 for PET, BOPP, and PE plastic films, (pendant drop method). respectively. The printing plate, made of a photopoly- The printability of polymer bases depends on mer prepared by the digital laser photochemical wettability of the bases by the printing ink. Further- method, had dimensions of 260 9 90 mm and a thick- more, the wettability of the base by the inks influences ness of 1.7 mm. The pressure between the anilox the adhesion between the base and the dried ink layer, 3 2 engraved roller (6 cm Æm volume, resolution or line the print quality, and mechanical properties of prints. ruling of 160 lines per cm ) and the plate cylinder was 98. All factors were kept constant during the printing process (printing speed, anilox roller, and printing 70 33 pressure). Printing was performed under controlled 64.7 environmental conditions of 23C and 50% relative 58.0 humidity (RH). 52.4 The optical densities of full-tone area, 75% tone 32.0 fields, L*, a*, b* measurements, and gloss of prints 11,12 were precisely described in previous works. The 37.7 optical densities of the full-tone area and specific ink 34.5 color components L*, a*, b* were determined using a 31.8 31 30.7 29.5 SpectroEye spectrophotometer (GretagMacbeth, 30 27.1 Switzerland). Measurements of the optical density of the full-tone area were taken at the following settings: 30.2 D50 illuminant using a 2 observer, 0/45 measuring 29.9 geometry, with a polarization filter, white standard: proofing paper. The measurements of L*, a*, b* were taken using these settings with absolute as a white 0 29 standard according to ISO standard. The reported FlexiWet FlexiWet + 1% PG-1,2 FlexiWet + 1% PG-1 results are the average of the measurements from a Prinng ink minimum of six areas on two different prints. BOPP PE PET Surface The gloss (in the gloss units, GU) of the prints was measured at 20,60, and 85 geometry conditions with Fig. 2: Properties of investigated printing inks: contact the use of a Picogloss (BYK-Gardner, Germany). Data angle and surface tension measured at t =23C for the original flexographic printing ink and after the addition of collection was performed at six different positions of polyglycerols the samples in both directions: cross and machine Contact angle (°) Surface tension (mN/m) J. Coat. Technol. Res., 15 (3) 649–655, 2018 5 70 Better wettability (so smaller values of contact angles) should indicate better adhesion of the ink layer to the base. The wettability may be estimated as a direct measurement of the static contact angle of the ink on the base. The contact angle together with surface tension of the ink without and with the addition of 2.72 investigated polyglycerols is shown in Fig. 2. The 2.67 2.58 addition of PG-1 decreases the contact angle of the 2.33 ink; therefore, an improvement of the wettability is 2.02 1.98 1.82 1.71 1.69 observed. The addition of PG-1 decreases the contact angle from 29.5 to 27.1.4, from 58.0 to 52.4, and from 34.5 to 30.7, for the BOPP, PE, and PET plastic film, respectively. In general, the addition of PG-1 decreases the contact angle about 9–12%. On the other hand, the addition of PG-1,2 increases the 0 30 contact angle of the ink. The higher contact angles FlexiWet FlexiWet + 1% PG-1,2 FlexiWet + 1% PG-1 are observed for the PE plastic film, and the lower Prinng ink contact angles for the BOPP plastic film. BoPP PE PET Gloss BoPP Gloss PE Gloss PET The surface tension of the ink slightly increases with an increasing mass fraction of polyglycerols. The Fig. 3: Optical densities of full-tone area and gloss of ink highest value of surface tension was observed for the layers printed with the investigated printing inks printing ink containing PG-1 (32.0 mNÆm ), which is higher than surface tension of solvent-based inks we 11,12 ink layers. It is well known that the thickness of the previously observed. Hence, the values of surface dried ink layer depends on the wettability of the base tension are higher than the surface free energy of by the ink during the printing process. Better wetta- typical plastic films, i.e., the surface free energy of bility is connected with a thinner dried ink layer and untreated PE and BOPP is lower than 30 mJÆm ,as lower optical density, assuming constant division of the reported in the literature. The printing process ink in the inking unit during the printing process, not requires that the surface tension of the printing ink is influenced by the used additive. The optical density of lower than the surface free energy of the plastic film. full-tone area decreases with the addition of the PG-1. On the other hand, values of optical density of prints overprinted with the ink with the addition of PG-1,2 Print quality are higher than for originally printing ink or ink with the addition of PG-1. However, it should be mentioned The print quality was determined as the properties of that all optical density values are high. The flow curves the print, i.e., the optical density of the full-tone area, of printing inks were presented by us previously ; the the optical density of 75% tone fields, the color values presence of polyglycerols had a noticeable effect on the (L*, a*, b*), and gloss. flow curve. This effect is strongly related to contact Before print quality measurements are taken, the angle of the printing ink on the printing base. It might adhesion of the dried ink film should be quantified by 30,31 be connected with the greater capacity of primary simple adhesion test (tape test). Adhesion of the hydroxyl groups in the macromolecule for hydrogen original ink to BOPP and PE base was generally much bonding. The incorporation of secondary hydroxyl better than adhesion on a PET film. The adhesion of groups into the branched molecule of polyglycerol the dried ink film modified with obtained polyglycerol unfavorably affects the wettability effect of the printing was noticeably better. However, the values of contact ink, and the contact angle is higher together with angles on the plastic films indicate that the better optical density of full-tone area and gloss. adhesion to the BOPP or PET than to PE film is Gloss is one of the most important parameters in expected. Probably, the interaction between the dried printing and packaging technology, because gloss ink film and the top layer of PET film is quite poor. affects the print quality by providing a better overall The indirect method of assessing adhesion may be the look and greater depth to colors. Gloss is a property measurements of abrasion resistance. The dry and wet of a material that is responsible for light reflection from abrasion resistance of overprinted PE, BOPP, and PET a surface. The methods for measuring gloss depend on base by printing ink containing PG-1,2 is visibly worse the kind of base that is used. The original FlexiWet than prints overprinted with original printing ink or printing ink is a middle–high gloss, so the gloss values printing ink with the addition of PG-1. were in the range 30–70 gloss units (GU). Hence, a The values of optical density of full-tone area, measuring geometry with an angle of 60 was used optical density of 75% tone fields, relative printing according to the ISO standard. In general, the contrast, and gloss are listed in Fig. 3. The optical addition of polyglycerols to the FlexiWet printing ink density assesses the thickness of the dried ink layer. increases the gloss of the prints. This effect is stronger Higher values of optical density refer to thicker dried Opcal density Gloss J. Coat. Technol. Res., 15 (3) 649–655, 2018 Table 1: L*, a*, b* values and total color difference DE of ink layers printed with the investigated printing inks ab Printing ink L* a* b* DE ab BOPP FlexiWet 2.58 0.77 0.87 FlexiWet + 1% PG-1,2 1.44  0.03  0.46 1.9 FlexiWet + 1% PG-1 5.97 2.04 3.26 4.3 PE FlexiWet 9.70 0.33 0.50 FlexiWet + 1% PG-1,2 19.36  0.19  0.29 9.7 FlexiWet + 1% PG-1 5.04 1.56 2.38 5.2 PET FlexiWet 2.01 0.32 0.27 FlexiWet + 1% PG-1,2 1.62  0.04  0.19 0.7 FlexiWet + 1% PG-1 6.87 2.11 3.63 6.2 for the PG-1 than for PG-1,2. The differences are in the Obtained polyglycerols PG-1,2 and PG-1 exhibited range of 12.1 GU for BOPP prints, 5.1 GU for PE irregular structure containing primary and secondary prints, and 7.2 for PET prints for the printing ink hydroxyl groups or predominantly primary hydroxyl containing PG-1. The gloss of the prints is also related groups in the macromolecule, respectively. Polyglyc- to better wettability of the printing ink and smoothing erols were synthesized by ring-opening polymerization process of the printing ink while drying. using trimethylolpropane as a starting material. The color values (L*, a*, b*) together total color The impact of the polyglycerols on the wettability, differences are presented in Table 1. The total color surface tension, optical density, and color parameters differences (DE ) were calculated from equation : (L*, a*, b*) is reported in this paper. The addition of ab branched polyglycerols strongly affects the wettability qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi of the base by printing ink. Furthermore, the wettabil- 2 2 DE ¼ ðDL ÞþðDa Þ þðDb Þ ab ity of the ink on the film influences the print quality. We have proven that polyglycerols containing pre- where DL*, Da*, and Db* are the differences between dominately primary hydroxyl groups in the macro- the value of the ink with the addition of polyglycerols molecule have improved the print quality of the prints. and the original ink. The L* value is a measure of the Our results help to understand phenomena which lightness of an object and is quantified on a scale where occur during printing, support the use of branched L* = 0 for a perfect black diffuser and L* = 100 for a polyglycerols as performance additives for water-based perfect reflecting diffuser. For BOPP and PET printing printing inks, and may open up new possibilities for bases, the values of L* decrease with the addition of applications of these environmentally friendly poly- PG-1,2 and increase with the addition of PG-1. This mers. effect is strongly connected with optical density and the thickness of the dried printing ink. The thinner layer of Acknowledgments Funding for this research was printing ink is related to the ‘‘lighter color’’ of the ink. provided by National Science Centre of Poland based Therefore, low values of total color difference (DE ) on decision nr DEC-2013/11/D/ST8/03371. ab are observed for the printing ink with the addition of PG-1,2; the values are lower than 2, demonstrating that differences occurred but it cannot be observed with the Compliance with ethical standards human naked eye. Furthermore, higher values of DE ab are observed for the printing ink with the addition of Conflict of interest The authors declare that there is PG-1, due to the thinner printing ink layer. The no conflict of interests regarding the publication of this overprinted PE base was characterized by very poor paper. print quality, and the values of color values (L*, a*, b*) and total color differences are quite high. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/li censes/by/4.0/), which permits unrestricted use, distri Conclusions bution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and In this work, we have demonstrated the wettability the source, provide a link to the Creative Commons effect of branched polyglycerols and the impact of license, and indicate if changes were made. primary and secondary hydroxyl groups on wettability. 654 J. Coat. Technol. Res., 15 (3) 649–655, 2018 18. Zolek-Tryznowska, Z, Tryznowski, M, Izdebska, J, ‘‘Diglyc- References erol as an Environmentally Friendly Performance Additive for Water-Based Flexographic Printing Inks.’’ Przemysl 1. Seiler, M, ‘‘Hyperbranched Polymers: Phase Behavior and Chemiczny, 93 (11) 1970–1973 (2014) New Applications in the Field of Chemical Engineering.’’ 19. 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Journal

Journal of Coatings Technology and ResearchSpringer Journals

Published: Mar 12, 2018

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