EFFECT OF TENSILE STRENGTH BY VARIATIONS IN PEEL STRENGTH IN LAMINATED FILM FOR LIQUID PACKAGE

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1 Advanced Materials Development and Performance (AMDP211) International Journal of Modern Physics: Conference Series Vol. 6 (212) World Scientific Publishing Company DOI: /S EFFECT OF TENSILE STRENGTH BY VARIATIONS IN PEEL STRENGTH IN LAMINATED FILM FOR LIQUID PACKAGE Yukihiko MACHIDA Quality assurance Department, Taisei Lamick co., ltd., Shimo Ohsaki, Shiraoka machi SAITAMA, , JAPAN machida@lamick.co.jp Akira SHIMAMOTO Saitama Institute of Technology, 169, Husaiji, Fukaya city SAITAMA, , JAPAN Hiroyuki AOKI Machine and development department, Taisei Lamick co., ltd., Shimo Ohsaki, Shiraoka machi SAITAMA, , JAPAN Katsunori FUTASE Yushin co., ltd., Higashi uradate, Sanjo city NIIGATA, , JAPAN Good tensile strength of a laminated film for packaging is an indispensable property in preventing leakage. It is known that the peel strength between laminated film layers is closely related to the tensile strength of the film. In this study, we have measured the tensile strength for various peel strengths of two kinds of three layered laminated film; Nylon + Aluminum + Polyethylene and Nylon + Polyester + Polyethylene. These films have two peel layers, so we escalated one peel strength and fix another one. Then we found that the peel strength between the sealant and the boundaries strongly influences the tensile strength. About Nylon + Polyester + Polyethylene film, we researched applied amount of adhesive and observed cross section of specimen at measurement of peel strength. Then we found that there is difference in specimen condition at measurement of peel strength, and examined about relationship of peel strength and stiffness of specimen. Keywords: Tensile strength; Peel strength; Laminated film. 1. Introduction In recent years, the reduction of waste in daily life has become an increasingly serious problem, and traditional glass bottles and molded plastic packages are being replaced with plastic film to reduce the weight of the waste. Under the background, the new approach on the strength of plastic film to protect the contents is required. In the cases where the contents are a liquid, normally, a two to four-layer laminated film is used and shaped into pouches by heat sealing. In general, the strength of the 467

2 468 Y. Machida et al. laminate film is defined as the breaking strength per unit width of the heat sealing area 1. However, in this study, we defined the breaking strength to be the tensile strength. If the tensile strength is insufficient, the pouch will break and leak during distribution after packing. It is known that tensile strength depends on the heat plate temperature as well as the pressure and length of heat sealing 2-6. Additionally, it is expected that tensile strength is influenced by the peel strength between each layer. In addition, the thickness of the sealant layer that is melted during the heat sealing process to form the seal is generally 4 to 5 m, but the effect of different sealant layer thicknesses on tensile strength and the peel strength between each layer is still unknown. In this study, we measured the tensile strength of each thickness and peel strength between layers, and defined the effects that the materials and thicknesses had on peel strength and tensile strength. Furthermore, we considered ways to decrease the occurrence of liquid pouch breakage. 2. Test Specimens and Methods 2.1. Specimens Specimens used in this study were two kinds of laminated film, each having a three layer structure, that are generally used as pouches for liquids. The structures of the specimens were: (a) biaxially-oriented nylon 15 m + aluminum 7 m + low density polyethylene and (b) biaxially-oriented nylon 15 m + biaxially-oriented polyester 12 m + low density polyethylene. In addition, we used specimens with a polyester thickness of 4 m and 5 m. Fig. 1 shows the cross sectional view of the films. We used a polyester series adhesive to laminate each layer and laminated the layers using the dry lamination method. We applied the adhesive to one material with a barcoater dried the adhesive with a heater and then pressed the mating material onto the adhesive surface with a roller.the adhesive was diluted with ethyl acetate, which allowed us to change the peel strength of each boundary by varying the dilution rate to change the amount of adhesive applied.in this study, we held the peel strength of the boundary between the first layer (nylon) + second layer (aluminum or polyester) or the second layer + third layer (polyethylene) constant while changing the peel strength of the other boundary. The laminated film was sealed with a heat seal device (TP-71-B model by Tester Sangyo co., ltd.). The heat sealing parameters used were based on the test method for plastic film food packaging 7. The laminated film specimen was folded and sealed between two heat sealing bars heated to a temperature of 16. The specimen was sealed at a sealing pressure of.196mpa and sealing time of one second Test Method In this study, we used an INSTRON/33R-4465 (tensile and pressure tester, maximum capacity of 1N) tensile tester. The tension rate was 5mm/min, and the distance between the two chucks was 5mm. We defined the tensile strength to be the maximum load until breaking.

3 Effect of Tensile Strength by Variations 469 The peel strength was measured according to the T-shape peel method using a 15mm wide specimen that was fixed between two chucks. The upper chuck was raised at a steady rate of speed, and both the peel strength and peeling state were observed 8. Fig. 2 shows the outline drawings of the tensile strength and the peel strength test. (a) (b) Nylon 15 m chuck(movable) Fig.1 Cross section of a specimen 3. Results and Discussion Aluminum 7 m or Polyester 12 m Polyethylene Heat seal area (a) For tensile strength specimen chuck(still) 3.1. Tensile strength and peel strength of Nylon + Aluminum + Polyethylene (b) For peel strength Fig.2 Measurement methods Fig. 3 shows the relationship between tensile strength and peel strength measured in each specimen. In the result, black diamond mark indicates the results where only the peel strength between the first / second layers (boundary A) was changed, and white square mark indicates the results where only the peel strength between the second / third layers (boundary B) was changed. As can be seen in Fig. 3 (a), which shows the results for the 4 m polyethylene layer specimen, the maximum tensile strength was 43N at a peel strength of 3N in boundary A, and the tensile strength decreased as the peel strength weakened. On the other hand, when the peel strength of boundary B was increased above 4N, the maximum tensile strength remained almost constant (43N), and we confirmed that when the peel strength was decreased to less than 4N, the peel strength-tensile strength relationship followed the same trend as in boundary A, which is that the tensile strength decreased as the peel strength weakened. Fig.3 (b) is the result from polyethylene layer specimen of 5 m thickness. Same trend was observed with that of 4 m specimen. Furthermore, we confirmed that when the peel strength of boundary B was increased to more than 3N, the tensile strength in the 5 m polyethylene layer specimen was 47N, as opposed to 43N in the 4 m polyethylene layer specimen. When the peel strength was less than 3N, changing the peel strength of boundary A resulted in higher tensile strength than changing boundary B at the same peel strengths. Then, we observed the destruction point of the heat sealed area, the results of which are shown in Fig. 4. In the pictures, (a) is the destruction of boundary A, and (b) is the

4 47 Y. Machida et al. destruction of boundary B. When the peel strength of boundary A was changed, all destruction occurred at boundary A. On the other hand, when the peel strength of boundary B was changed, the destruction occurred at boundary A when the peel strength of boundary B was more than 4N, from which point the tensile strength remained constant, and all other destruction occurred at boundary B when the peel strength of boundary B was less than 4N.It is presumed that the destruction of boundary A occurs through the breakdown of the aluminum, thereby resulting in a higher tensile strength compared to the destruction of boundary B. Therefore, we have confirmed that in order to increase tensile strength, it is necessary to have a higher peel strength at boundary B than boundary A (refer to Fig. 3). Heat seal strength(n) Nylon/aluminum (A) aluminum/polyethylene (B) Adhesive strength(n) (a) Polyethylene 4 m (a) Destruction at boundary A Fig.4 Two types of destruction 3.2. Tensile strength and peel strength of Nylon + Polyester + Polyethylene Fig. 5 shows the relationship between tensile strength and peel strength measured in each specimen. Fig. 5 (a) shows the 4 m polyethylene layer specimen, and (b) shows the 5 m layer specimen. From Fig. 5 (a) and (b) it can be seen that when the peel strength of boundary A was changed, the maximum tensile strength was 61 N in the 4 m polyethylene layer specimen and 63 N in the 5 m polyethylene layer specimen. We confirmed that the tensile strength decreased in association with a decrease in peel strength. We believe that the destruction occurs at boundary A as a result of varied peel strength at boundary A (refer to Fig. 4 (a)). On the other hand, when the peel strength of boundary B was changed, the tensile strength decreased even with an increase in peel strength. Next, we looked in the amount of adhesive applied to a 4 m polyethylene layer specimen. The results are shown in Heatseal strength(n) Fig.3 Peel strength and Tensile strength Nylon/aluminum (A) aluminum/polyethylene (B) Adhesive strength (N) (b) Polyethylene 5 m (b) Destruction at boundary B

5 Effect of Tensile Strength by Variations 471 Fig. 6. As can be seen in Fig. 6 (a) and (b), although the tensile strength increases as the amount of adhesive applied is increased, the peel strength decreases. Then, we used an optical microscope to observe the cross sections of specimens after measuring peel strength, the results of which are shown in Fig. 7. Fig. 7 (a) shows the cross section a specimen to which 1.7g/m 2 of adhesive was applied, and (b) is the cross section of a specimen to which.8g/m 2 of adhesive was applied. As can be seen in these pictures, the destruction at boundary B occurred between the polyester layer and adhesive, and there was almost no deformation in the polyethylene after peeling in the 1.7g/m 2 specimen while plastic deformation was observed in the.8g/m 2 specimen. Tensile strength(n ) Heat seal strength(n) Nylon/polyester(A) Polyester/polyethylene(B) Adhesive strength(n) (a) Polyethylene 4 m 1 2 Adhesive quantity (g/m 2 ) (a) Adhesive quantity and tensile strength Fig.5 Peel strength and tensile strength Adhesive strength(n) (b) Polyethylene 5 m In the case of the.8g/m 2 specimen, because the adhesive layer on the polyethylene layer is thin, the cross-section area of specimen is also small, and the lower elastic modulus in the adhesive + polyethylene layer decreases the stiffness, resulting in peeling that occurs with plastic deformation. Then, we studied the peel angle. From the results, we learned that the peel angle in specimens with a small amount of adhesive applied is larger than in specimens with a large amount of adhesive applied. It is thought that this occurs due increased peel strength in specimens with a small amount of adhesive applied as the peeling in such specimens occurs along with plastic deformation of the polyethylene layer. Therefore, in order to obtain high tensile strength, it was confirmed that the amount of adhesive applied to boundary B needs to be increased. Also, we confirmed the positive effects of polyethylene thickness on tensile strength based on the results indicating a maximum tensile strength of 61N in the 4 m Peel strength(n) Adhesive quantity(g/m2) Fig.6 Relationship between adhesive quantity and strength Heat seal strength(n) Nylon/polyester(A) Polyester/polyethylene(B) (b) Adhesive quantity and peel strength

6 472 Y. Machida et al. polyethylene layer specimen and 63N in the 5 m polyethylene layer specimen, which is also the same trend found in the specimen of nylon + aluminum + polyethylene. (a) The case of high coated adhesive (b) The case of low coated adhesive Fig.7 Cross section of specimen at measurement of peel strength 4. Conclusions As a result of this study on the effects of peel strength on tensile strength in laminated films, we learned the following: (i) The tensile strength of laminated film is affected by the peel strength of each boundary in the film. (ii) Irrespective of the specimen, if the peel strength of boundary A is reduced, the tensile strength decreases. (iii) In the case of nylon + aluminum + polyethylene, the tensile strength is higher at the same peel strength when the peel strength of boundary A is changed as opposed to when the peel strength of boundary B is changed. Therefore, in order to obtain high tensile strength, the peel strength of boundary B needs to be increased. (iv) In the case of nylon + polyester + polyethylene, when the amount of adhesive applied to boundary B is increased, the tensile strength increases, but peel strength decreases. Therefore, in order to obtain high tensile strength, the amount of adhesive applied at boundary B needs to be increased. References 1. Japanese Standards Association: JIS Handbook, Adhesion, JIS Z238 (1999), P Futase, K., The Society of Packaging Science and Technology, Vol.14,No.6(25),P Futase, K, Shimamoto, A, Takahashi, S, Journal of the Japan Society of Mechanical Engineer, 6A (1994), P Aoki, H., Shimamoto, A., Futase, K., Kamada, Y., APCFS & ATEM 1, JSME-MMD, Oct (21), Futase, K, Shimamoto, A, Takahashi, S, Journal of the Japan Society of Mechanical Engineer, 6A (1994), P Futase, K., Shimamoto, A., Takahashi, S., Aoki, H., : Journal of the Japan Society of Mechanical Engineer, (1991), P Japanese Standards Association: JIS Handbook, Plastic ⅠJIS K 7113 (29), P Japanese Standards Association: JIS Handbook, Adhesion JIS K 6854(1999), P