The Effect of SI Diblock in SIS Block Copolymer on Pressure-Sensitive

Chapter 8

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 8, 2015 | http://pubs.acs.org Publication Date: June 30, 1998 | doi: 10.1021/bk-1998-0696.ch008

The Effect of SI Diblock in SIS Block Copolymer on Pressure-Sensitive Adhesive Properties Tetsuaki Matsubara and Minoru Ishiguro Research and Development Center, Nippon Zeon Company, Ltd., Kawasaki 210, Japan

We found that Styrene-Isoprene (SI) diblock in Styrene-Isoprene-Styrene (SIS) copolymer improves carton sealability which is one of the important properties of carton sealing tapes. Diblock copolymer reduces storage modulus of adhesive compound. The low modulus gives poor shear adhesion but improves wettability to rough surface which seems to be a predominant factor on carton sealability.

SIS block copolymers produced by living anionic polymerization technique are applied in the largest volume to pressure sensitive adhesive (PSA) tapes, especially to carton sealing tapes. The copolymers produced by coupling method, which is the most commonly used in commercial production processes, contain some uncoupled SI diblock copolymers. There have been some studies of the effect of diblock in SIS copolymers on adhesive properties (7-2). However, the effect on carton sealability has not been discussed while unfolding failure of a carton boxes sealed with a tape is the most serious problem. In this paper, the effect of diblock content in SIS on PSA properties, especially on carton sealing properties, is discussed from rheological viewpoints. Experimental Section Three commercial SIS block copolymers were investigated in this study. They are produced by a traditional coupling method which consists of sequential polymerization of styrene and isoprene, and a coupling reaction. 98

©1998 American Chemical Society

In Applications of Anionic Polymerization Research; Quirk, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.


99 SIS Block Copolymers. The molecular characteristics of the three copolymers are shown in Table I. They are similar in styrene content and Mw which represents overall weight average molecular weight, but not in SI diblock content. It should be noted that the same Mw does not mean the same GPC peak top molecular weight of SIS triblock. Though both of Quintac 3422 and Quintac 3520 have the same Mw, the molecular weight of diblock copolymer or its coupled triblock copolymer in Quintac 3520 is considerably higher than each corresponding molecule of Quintac 3422. Because Quintac 3520 contains much more amount of diblock copolymer whose molecular weight is equal to a half of that for coupled triblock copolymer (Figure 1).

Table I. Molecular Characteristics of the Investigated Polymers Quintac 3520 POLYMER Quintac 3433 Quintac 3422 15 16 15 Styrene Content [wt%] 78 SI Diblock Content 52 [wt%] 10 200 Mw 170 [xlO ] 200 Overall weight average molecular weight determined with Gel Permeation Chromatography (GPC) which is calibrated with polystyrene standard. a

3

Measurements of PSA Properties. In order to evaluate PSA properties, the SIS copolymers were compounded with an aliphatic hydrocarbon resin with softening point of 96°C (Quintone R100) and a naphthenic process oil (Shellflex 371N). The PSA compounds were coated on a 25 μηι polyester film with coating thickness of 25 μηι. The PSA properties were measured in accordance with PSTC (Pressure Sensitive Tape Council) standard (3) except carton sealability which was developed by ourselves. Tack. A PSA tape specimen was arranged adhesive side up in line with the raceway of the PSTC standard incline so that it was free of any wrinkles, creases, or splices. The end of the tape opposite the incline was held to the table with a weight. A steel ball with 14/32 inch diameter was placed on the upper side of the incline. The ball was released and allowed to roll to a stop on the adhesive. This property was measured at 23 °C. Tack is expressed in terms of the average of the stopping distance which was determined through five tests for each tape specimen, (unit: mm). Peel Adhesion (Adhesive Strength). A PSA tape specimen with width of 10mm was stuck on a stainless steel plate. After dwell time of one hour, the tape was peeled off at 23°C in a direction of 180° at a rate of 300mm/min.(unit: g/10mm).


100


Holding Power (Shear Adhesion). A PSA tape specimen was stuck on a stainless steel panel with contact area of 25mm>v

^^Formulation 1

Formulation 2 ^ \ ^

3

10 l 10"

2

ι ΙΟ"

1

ιI 10°

I Quintac 3520 Basel . ι1.... 1 10 10 1

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TIME [s]

Figure 13. Stress relaxation curve of adhesives


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Because, the repelling force of carton boxes is not constant, and because the contributing ratio of carton sealability and holding power to total sealing properties may vary with the dimension of a carton box, width of a tape and length of tape ends applied to both sides of a box. But we can point out that a PSA based on a conventional SIS with low diblock content is generally hard, difficult to deform and poor in wettability. Acknowledgments We would like to thank Mr. M . Nakamura of Nippon Zeon Co. Ltd. for useful discussions. References 1. Johnsen, Κ. E. Adhesives Age 1985, 29. 2. The Effect of Diblock on Pressure Sensitive Adhesive Properties; Dillman, S. H.; PSTC Technical Seminar Proceedings, 1991. 3. Test Methods for Pressure Sensitive Adhesive Tapes, 10th Edition, Pressure Sensitive Tape Council, 1992. 4. The Effect of Diblock on Carton Sealability of Packaging Tape; Ishiguro, M.; PSTC Technical Seminar Proceedings, 1995. 5. Parsons, W. F.; Faust Μ. Α.; Brady L. E. J. Poly. Sci.; Poly. Phys. Ed. 1978, 16, 775. 6. Aubrey D. W. J. Poly. Sci.; Chem. Ed. 1980, 15, 2597.


The Effect of SI Diblock in SIS Block Copolymer on Pressure-Sensitive

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