VOL 18 NO 1

Pore Structure Characterization of Barrier Coatings for and Paul D. Fleming III and Margaret K. Joyce Center for Coating Development Department of Paper and Imaging Western Michigan University

estern Michigan numerous other applica- turers. An impregnator, WUniversity has ac- tions where a product in essence, is a shoe press tive research character- must be protected from with a pressurized coat- izing coatings for paper the ambient environment, ing delivery system. To and paperboard which or vice versa(1-4). Barrier impregnate the sheet, the provide barriers for gases packaging materials and coating is put under pres- and liquids in addition to coatings include not only sure, 10-100 psi, and then printable surfaces. Bar- the obvious materials forced into the sheet as it rier-coated packaging is and coatings necessary passes through the shoe an extremely large and for barrier properties, but (nip). Controlled penetra- important area of interest also those needed for the tion depths of 20-80% are to industry(1-4), govern- and converting. typical and have found ment(5,6), and the con- Our research on barrier commercial benefits to sumer(1,2). It is expected coatings has been facili- corrugated board manu- to grow rapidly as indus- tated by our extensive facturers seeking strength try expands its market measurement capability and stiffness improve- offerings of ethnic and for coated and printed ments while leaving one specialty foods, nutra- paper. We can determine side available to bond to ceuticals and functional flow (fluid permeability) the medium. foods, extended shelf life characteristics(11), mois- The essential raw mate- products(7-9), and conve- ture vapor transmis- nience foods and prod- rial of nano-clay is mont- sion(12), macro and micro ucts. Consumers are de- morillonite, which is a 2:1 roughness(13,14), and pore manding longer shelf life, layer smectite clay min- size and surface area(15,16) eral with a platey struc- safe(5), and added value associated with barrier ture. Individual platelet packaged products(10). To coatings. The latter capa- package these products, thicknesses are just one bility regarding pore prop- there is a need for better nanometer, but surface erties is facilitated using barrier systems due to dimensions are generally Micromeritics’ TriStar gas the conversion of many 300 to more than 600 nm, adsorption and AutoPore product applications from resulting in unusually IV instruments. rigid container to flexible high aspect ratios. The as- container systems. Recently, we compared pect ratio is defined as the particle’s length-to-thick- the use of impregnation(15) Barrier packaging is used to apply a barrier coating ness ratio. Most clays in multi-layer food pack- containing nanosized clay used in paper coatings are aging (a “juice box” is one reported as having aspect particles(17) to application example), microwavable with a conventional size ratios ranging from 10-25. popcorn bags (grease Nano-clays have aspect press(18). Impregnation proof paper used for pack- technology is currently ratios ranging from 150- aging popcorn is one ex- being used by flooring, 400. ample), in “quick service” molding compound, im- wrapping paper (a fast- Four different coatings pregnated textiles, and food hamburger wrap- were prepared with a low decorative film manufac- per is one example), and molecular weight ethyl-

4 VOL 18 NO 1

ated starch, Penford Gum 290. The nano-clay was 0.07 added to determine its in- fluence on the porosity of 0.06 the paper in comparison to just starch alone. All 0.05 coatings were applied at approximately 20% solids 0.04 at 90° F. The viscosities of the coatings were all 0.03

below 100 cP. The coat- Intrusion (mL/um) Differential ings were applied to an 0.02 unsized (HST 0.4 sec), 70 0.01 g/m2 unbleached Kraft basepaper using an im- 968.82 pregnator coater. 0

90.72 45.27 30.23 21.34 8.06 6.03 0.08 0.03 0.008 0.003 0.001 The pore size of the un- -0.01 306.65 13.95 treated basepaper was Pore Size Diameter (micrometer) analyzed using a Mi- Figure 1. cromeritics AutoPore IV Pore size distribution of base unbleached obtained mercury porosimeter. from a Micromeritics AutoPore IV Mercury porosimeter. After treatment, resulting pores were analyzed using a Micromeritics TriStar BET gas adsorption ana- lyzer. The basepaper pore 0.0040 size distribution is given in Figure 1. 14 gsm SP 0.0035 After coating, the pore 6 gsm SP

/g) size was reduced so much 0.0030 3 6 gsm Impreg that Hg gave no useful results, so the TriStar was 14 gsm Impreg used with nitrogen gas to 0.0025 determine the pore size distributions of the coated 0.0020 paper. These are shown (cm Pore Volume in Figure 2 for two differ- 0.0015 ent coat weights applied with the impregnator compared with the same 0.0010 coat weights applied with a conventional flooded nip 0.005 size press (15,18). Note the extremely small volume 0 of pores between 1 and 10 10.0 100.0 nm for the impregnated Pore Diameter (nanometer) relative to the size Figure 2. press treated samples. Pore size distribution of impregnator-coated and size press- The highest coat weight with two different coat weights. also shows a smaller tail on the pore size distribu- tion of the base paper (Figure 1). This is indica-

5 VOL 18 NO 1

tive of the very effec- 23-28, 2002. tive barrier properties 9. A. Begin and Sean Bouchard, “Control of the Effect of Ethylene on of these coatings. This Maturation of Tomatoes Packed in is corroborated in the Modified Atmosphere. Initiation of measurement of other Oxygen, Carbon Dioxide and Ethyl- ene and Mathematical Model Devel- (15) barrier properties . opment,” International Association Because of these sorts of Packaging Research Institutes of characterizations (IAPRI)-WORLDPAK Conference. East Lansing, MI, June 23-28, 2002. of barrier coatings of 10. P. Joshi, “Active Plastics Pack- paper and paperboard, aging,” International Association of Western Michigan Uni- Packaging Research Institutes (IA- PRI)-WORLDPAK Conference. East versity, in collaboration Lansing, MI, June 23-28, 2002. with Michigan State 11. Lokendra Pal, Margaret K. University, has been Joyce and P. D. Fleming, “A Simple Method for Calculation of Perme- chosen by the National ability Coefficient of Porous Media,” Science Foundation to TAPPI J., August 2006. establish the Barrier 12. Lokendra Pal, Margaret K. Joyce, Paul D. Fleming, and David Packaging Materials E. Knox, “Shape Engineered Pig- and Coatings Center as ments Based Barrier Coatings for an IUCRC (Industrial SBS Paperboard,” manuscript in preparation. University Cooperative 13. Renmei Xu, Paul D. Fleming III, Research Center) site(19). Alexandra Pekarovicova, and Valery This Center will serve Bliznyuk, “The Effect of Ink Jet Papers Roughness on Print Gloss as a focal point for bar- and Ink Film Thickness,” J. Imag- rier packaging research ing Sci. Technol., 49 (6), Nov. / Dec. in collaboration with 2005, 660-665. 14. Renmei Xu, Alexandra Pekarov- suppliers and consum- icova, Paul D. Fleming, and Valery ers of these materials. Bliznyuk, “Physical Properties of LWC Papers and Gravure Ink Mileage,” Proceedings of the 2005 TAPPI Coating & Graphic Arts Conference, April 17-20, in Toronto, References ON, Canada. 15. Margaret K. Joyce, Thomas W. AutoPore IV Mercury Joyce, Kapil Thomas, Tanuj Bajaj, 1. C. P. Klass, “Emerging Barrier Porosimeter and Jatetana Kunsriluksakal, “Us- Coating Market Trends,” Bar- ing an Impregnation (Controlled rier Coating Symposium, Western Penetration) Method for Michigan University, Kalamazoo, Improving the Barrier and Strength MI, Oct. 8-9, 2002. 1, Part 109, 2002. Properties of Paper and Board,” 2. C. P. Klass, “Market Trends,” 6. U.S. Congress, Office of Tech- Invited Speaker, Internal and Sur- Barrier Coating Symposium, Kal- nology Assessment, Biopolymers: face Sizing PIRA Conference, Graz, amazoo, MI, Oct. 12-13, 2004. Making Materials Nature’s Way- Austria, 2003. 3. J. McCracken and V. Bell, Background Paper, OTA-BP-E-102, 16. D Jayaraman, M. K. Joyce and “Worldwide Environmental Packag- Washington, DC: U.S. Government T. W. Joyce, “Nano-Talc Pigment ing Mandates,” Barrier Coating Printing Office, Sept. 1993. Based Barrier Coatings,” Surface Symposium, Western Michigan 7. R. Alves and S. Jaime, “Stability Coatings International, Sept. 2003, University Kalamazoo, MI, Oct. of ‘Reqeijao Cremoso’ in Difference Vol. 86 Issue A07 p.281-284 Techni- 8-9, 2002. Packages at Dark Storage,” Inter- cal Updates. 4. J. McCracken, “Worldwide national Association of Packag- 17. http://www.nanocor.com/nano- Environmental Packaging Man- ing Research Institutes (IAPRI)- clays.asp. dates,” International Association of WORLDPAK Conference. East 18. Dale R. Dill, “Control and Un- Packaging Research Institutes (IA- Lansing, MI, June 23-28, 2002. derstanding of Size Press Pickup,” PRI)-WORLDPAK Conference. East 8. G. Mortensen and J. Sorensen, TAPPI J., 57(1): 97-100 (1974) Lansing, MI, June 23-28, 2002. “Reduction of Photo-oxidative 19. http://www.wmich.edu/pci/lat- 5. USFDA, “Unavoidable Con- Quality Changes in Cheeses by est/NSFIUCRC.html. taminants in Food For Human Proper Packaging,” International Consumption and Food-Packaging Association of Packaging Research Material,” Code of Federal Regula- Institutes (IAPRI)-WORLDPAK tions, Title 21, Volume 2, Chapter Conference. East Lansing, MI June

6