Physical properties of biaxially oriented PA6 film for simultaneous stretching and sequential processing

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1 J Polym Eng (): xxx xxx by Walter de Gruyter Berlin New York. DOI.55/POLYENG..5 Physical properties of biaxially oriented PA6 film for simultaneous stretching and sequential processing Q: Please supply full first name for T Kanai Q: No keywords were provided in the original paper. Please confirm if current keywords are correct Masao Takashige, * and T Kanai Idemitsu Unitech Co., Ltd., Shinkawa NS Bldg., 6-, Shinkawa-Chome, Chuo-ku, Tokyo, Japan, masao.takashige@iut.idemitsu.co.jp Idemitsu Kosan Co., Chiba, Japan *Corresponding author Abstract There are two different stretching processes that produce the biaxially oriented film, namely the tenter process and double bubble tubular film process. Furthermore, there are two tenter processes, i.e., the sequential biaxial stretching process and simultaneous biaxial stretching process. There is no report describing the difference among film physical properties of the three different processes. The biaxially oriented polyamide film using the double bubble tubular process has good balanced physical property and high impact strength, thus it is used for proper applications utilizing their advantage properties. In this report, the influence of each biaxial stretching process on film physical properties of polyamide, which has hydrogen bond, was studied in detail. As a result, the tentering process film has anisotropic tensile properties between machine direction () and transverse direction (). This result was influenced by a later stretching process, namely stretching. On the contrary, the double bubble tubular film has good balanced properties, especially thermal shrinkage and impact strength. Tentering simultaneous has much larger shrinkage in than in. The sequential has larger shrinkage in than in. The double bubble tubular film has high impact strength, because it corresponds to the balanced molecular orientation. Keywords: biaxially oriented film; machine direction; stretching process; transverse direction.. Introduction In recent years, the environmental problems have come into question in the packaging industry. These problems, such as the dechlorination and the waste reduction, have been closed up in this industry. The waste reduction especially has been a serious problem. To achieve this waste reduction, there is a rapid increasing shift from a one-way bottle to a standing pouch for repackaging use in an effort to utilize resources effectively. Biaxially oriented PA6 films, which are thin and strong, are indispensable for many applications. Several types of manufacturing processes have been developed to produce the biaxially oriented PA6 film featured by high strength. Among them, the double bubble tubular process producing biaxially stretched PA6 film is the best process in terms of impact strength. It is highly valued for the purpose of distribution of safety products. There are several reports published on the double bubble tubular stretching technologies [ ] of process abilities and structure analyses for resins such as PET, PBT, PPS, PA6- and PA reported by Kang et al., Song et al. and Rhee et al. [ ]. There are two different stretching processes that produce the biaxially oriented film, namely the tenter process and double bubble tubular film process [ ]. Furthermore, there are two tenter processes, i.e., the sequential stretching process and simultaneous biaxial stretching process. However, there are few reports on the double bubble tubular technology and the tenter biaxial stretching process. In general, the biaxially oriented PP film and PET film can be easily produced by the sequential stretching process. By contrast, as PA6 has hydrogen bond, it is hard to produce the biaxially oriented PA6 film by the sequential stretching process. The biaxially oriented PA6 film was firstly produced by the simultaneous biaxial stretching process developed by Unitika. Hitachi developed the simultaneous biaxial stretching machine using pantograph type and then Hitachi and Unitika have collaborated and produced the biaxially stretched film commercially []. Several years later, Toyobo developed the new type PA6 resin reduced hydrogen bond by using compounding technology [4]. The biaxially oriented PA6 film using the double bubble tubular film has good balanced physical property and high impact strength, thus it is used for proper applications utilizing their advantage properties [5 ]. There is no report clearly describing the difference among film physical properties of three different processes. In this report, the influence of each process on film physical properties was studied in detail.. Experimental.. process Apparatus used for the double bubble tubular film process is shown in Figure, taken from a previous report []. A 5 mm ϕ extruder (L/D = 5) with a circular die of a diameter of mm and a lip clearance of mm and with a water-cooling ring with a diameter of mm was used. While passing Q: Please ensure that all abbreviations/ acronyms are clarified on first citation, such as PET, PBT, PPS, PA6- and PA Q4: Please ensure that the name of the manufacturer, name of city and country are provided for all equipment/ instrument /5

2 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film Air ring Infrared heater Die Article in press - uncorrected proof Hopper Extruder sheet was stretched at.5.5 and a 5- µ m thickness film was obtained. The material used was an Ube PA 8FD (PA6) with a mean molecular weight of 9, and a relative viscosity of η r =. in 98 % sulfuric acid as a solvent. Q5: Please confirm if article/ running title is correct Heat treatment Second bubble Bubble through for second blowing, which is composed of two pairs of pinch rolls and a heating furnace (a far infrared radiation heater is self-contained), this raw film was stretched simultaneously in the machine and transverse directions by using internal bubble air. The stretched film was heat-set using a heat treatment device. The material used was an Ube PA FD (PA6) with a mean molecular weight of, and a relative viscosity of η r =.5 in 98 % sulfuric acid as a solvent. The experimental method of the double bubble tubular film is described in this section. The process conditions of the unstretched film were 7 C for resin temperature at the die exit,. for blow-up ratio, and 6. for draw-down ratio, respectively. The extrusion rate was 4 kg/h and the take-up velocity was 5.7 m/min. Film was quenched in water at C to suppress crystallization. The stretching device consists of a heating/stretching furnace and an air ring. The air ring, which injects air downward at an angle of, was installed at the upper part of the heating furnace. The standard condition for stretching process was set at C for process temperature (temperature of heating furnace), which means that the bubble temperature 58 C at the beginning point of the stretching zone and the bubble temperature 9 C at the end point of the stretching zone using the contact type thermometer. Machine direction/transverse direction (/) was set./. for stretching ratio. The stretched film was heat treated to prevent shrinkage, using a heat treatment device of the tenter process. The measurement method of stretching stress is described in a previous report []. Stretching stress was calculated with the aid of the tubular theoretical equation reported by Takashige and Kanai. The maximum stress at the end point of stretching could be obtained. Internal bubble pressure during the stretching was measured by using the digital manometer in the double bubble tubular process, and the stretching stress was calculated. Stretching stress in was 9 MPa... process First bubble Water cooling ring Figure Schematic view of double bubble tubular film process. The simultaneous stretching conditions were stretching ratios.5.5 at stretching temperature 8 C using Toshiba machinery which considered 75 ϕ Extruder, T-die 5 mm width chill roles and preheating and stretching zone. A 8- µm thickness.. process The sequential stretching conditions were stretching ratio.5 for and.5 for using the Plastics Kogaku Kenkyusyo 5 ϕ Extruder, 5 mm width T-die, chill role and the Nikko Seisakusyo stretching machine along the and then stretching tentering machine along the. The stretching temperatures were 75 C for and 8 C for. The material used was an Ube PA 5FD (PA6) with a mean molecular weight of 5,8 and a relative viscosity of η r =. in 98 % sulfuric acid as a solvent. The material used was a Mitsubishi Gas hemical MX PA 67 with a mean molecular weight of 5, and a relative viscosity of η r =.7 in 96 % sulfuric acid as a solvent. The blending ratio was fixed 5 % in MXD6. To compare the physical properties of double bubble tubular film with one of the tenter films, the commercially popular films produced by three different processes were used. As described above, there are two tentering oriented films, namely the sequential process and simultaneous tenter process. Two tentering oriented films (5 µ m), produced by the sequential process and simultaneous tenter process were obtained. The resin properties of each sample, such as relative viscosity, molecular weight, melting point and crystallization temperature, were measured. The quantitative analysis of relative viscosity was measured using 98 % solution of sulfuric acid. The molecular weight was estimated using relative viscosity. Table shows the resin properties of three different types of biaxially oriented films. From these results, double bubble tubular film used higher molecular PA6 than the tenter sequential. To keep the bubble stability, high molecular PA6 was used. Each film used silica for anti-blocking property..4. Mechanical properties The toughness was evaluated by using the film impact strength equipment with a / inch ball produced by Toyo Seiki Seisaku-syo, Ltd. The film impact strength was evaluated under the different temperatures in the room which could be controlled as the temperature of atmosphere ( - 5 C C). Tensile properties such as tensile modulus, tensile strength at break, elongation at break were measured at C, 5 % relative humidity, by the measurement methods of ASTM D-88 with Instron manufactured by Instron Japan..5. Shrinkage in hot water In the PA6 film for retort food, it is soaked in hot water of high temperature to conduct sterilization and processing. The

3 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film Table Resin properties of biaxially oriented PA6. Properties System Double bubble tubular process Tenter process Sequential biaxial Resin PA6 PA6 PA6 95 % MXD6 5 % Relative viscosity η r.5.. Molecular weight M n, 9, 5,8 Melting point C vs. sequential biaxial. Tubular process vs. tenter process. relationship among heat setting temperature, film shrinkage percentage and film density was examined. The shrinkage in hot water as a function of temperature was evaluated. Two different temperature conditions, namely hot steam condition C, min and hot water condition 95 C, min, were tested. By changing cross-direction position, the value of the shrinkage percentage pattern in-plane was measured. At first, the length of the gauge length L, which was every mm in-plane (,,, 5 ) before heat treatment, was marked. After heat treatment spread in hot steam condition of C for min or hot water condition 95 C for min, conditioning for 4 h under C, 5 % relative humidity was done and then the length of the marked gauge length L S was measured again. Shrinkage in hot water was defined in the following equation: S = (L -L S )/L % () where S is shrinkage in hot water, L is gauge length before heat treatment ( mm), and L S is gauge length after heat treatment..6. Stress-strain curve measurement Tensile properties such as tensile strength at break, elongation at break were measured at C, 5 % relative humidity, by the measurement methods of ASTM D-88 with Instron manufactured by Instron Japan. By changing the cross-direction position (,,, 5 diagonal angle), the value of the tensile strength pattern in-plane was measured. Film orientation is evaluated by using wide angle X-ray diffractometry produced by Rigaku (Rotary Flex RU-)..7. X-ray diffraction pattern Film orientation is evaluated by using wide angle X-ray diffractometry produced by Rigaku (Rotary Flex RU-)..8. Polarized fluorescence observation Molecular orientation in the amorphous region is evaluated by using polarized fluorescence observation. The film sample was immersed under C into the. % solution of a fluorescent substance (Sumitomo Chemical Whitex-RP) for 4 h. The polarization fluorophotometer which was FOM- manufactured by Jasco Corporation was used as a measuring instrument. The excitation light wavelength was 65 nm and fluorescence wavelength was 4 nm. The polarized fluorescence intensity in-plane (I and I ) as a function of angle which was measured by rotating a polarizer and an analyzer was obtained. I denotes that a polarizer and an analyzer are parallel. I denotes that a polarizer is perpendicular to an analyzer. The excitation light was entered from backside of the sample.. Results and discussion.. Film tensile properties Table shows the physical properties of three different types of biaxially oriented films. From these results, double bubble Table Physical properties of biaxially oriented PA6. Properties System Double bubble tubular process Tenter process Testing method Tensile modulus MPa ASTM-D88 7 Tensile strength at MPa ASTM-D88 break 9 7 Elongation MPa ASTM-D Film impact strength J/m 9, 58, 75, IPC method vs. sequential biaxial. Tubular process vs. tenter process.

4 4 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film tubular film has balanced physical properties. By contrast, the tenter sequential has anisotropic properties between and. The tensile strength at break in produced by sequential stretching process is higher than in. This result is owing to a stretching effect in which remained by the latest stretching. Interestingly, it was found that tensile modulus and tensile strength at break have an opposite trend between and. In the case of PA6, the tensile modulus is very much influenced by perpendicular to the stretching direction. By contrast, the tensile strength at break is influenced by the stretching direction. As this result is caused by the hydrogen bond, it is very much different from PET and PP... Film impact strength Impact strength is shown in Figure. The impact strength of double bubble tubular film has the highest value at all temperature ranges from -5 C to C. This result is owing to the high molecular weight and / balanced property which denotes multi-axis stretching and not biaxial stretching. The film impact strength increases with increasing the measured temperature for all samples. Furthermore, the impact strength of the double bubble tubular film at - C is stronger than the impact strength of the simultaneous tenter film at C C- min 95 C- min.. Shrinkage in hot water Heat shrinkage patterns are shown in Figure. Heat shrinkage pattern is influenced by the biaxial stretching process. The double bubble tubular film has balanced shrinkage pattern. Tentering simultaneous has much larger shrinkage in than in. By contrast, tentering sequential has larger shrinkage in than in. This result is owing to a stretching effect which is done at the latest 5 4, 9, Figure Shrinkage percentage pattern in hot water. Film impact strength (J/m) 8, 7, 6, 5, 4,, Temperature ( C) Figure Relationship between temperature and film impact strength. stretching. The shrinkage in hot water is related to the amorphous orientation..4. Stress-strain curve (S-S curve) Stress-strain patterns are shown in Figure 4. Stress-strain pattern is influenced by the biaxial stretching process. The double bubble tubular film has a balanced tensile property pattern. By contrast, the tenter stretched film shows an unbalanced tensile property pattern in film plane. This result is owing to the stretching effect which is called the bowing phenomenon. The bowing phenomenon is a serious technical problem that needs to be solved in the stretching of film which

5 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film 5 Stress (MPa) (MPa) Stress (MPa) Stress (MPa) Figure Strain Strain 5 causes the non-uniformity of film characteristics in the. The bowing phenomenon relates to the discrepancy between the orientation axes at the edge of film width, which causes the anisotropy of film characteristics such as heat shrinkage, refractive index and mechanical properties. The difference between the direction of the molecular orientation axis and the line direction becomes large towards the edge of film in the film width. The bowing phenomenon does not occur in the stretching process of the double bubble tubular process, owing to the no edge effect. By contrast, the tentering process has an edge effect. Reducing the bowing phenomenon is one of the most important technical issues in the manufacturing of biaxially oriented film Strain Stress-strain pattern in-plane. Figure 5 (MPa) 4 4 Tensile strength pattern in-plane. (MPa) The double bubble tubular film has a balanced stress-strain curve in each direction and high elongation at break, which gives good thermoformability. Tensile strength patterns in-plane are shown in Figure 5. Strain patterns (elongation) in-plane are shown in Figure 6. The double bubble tubular film also has a balanced tensile property pattern in-plane. By contrast, the tenter stretched film also shows an unbalanced tensile property pattern in film plane. In particular, tentering simultaneous has small strain patterns (elongation) in-plane. This property effect results in low impact strength and bad thermoformability..5. Wide angle X-ray diffraction patterns (molecular orientation in the crystalline region) Wide angle X-ray diffraction patterns are shown in Figure 7. These results show the different orientation patterns dependent

6 6 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film Meridian () Equator () θ/degree Meridian () Equator () θ/degree Meridian () Equator () Figure 6 Elongation at break pattern in-plane. θ/degree on the biaxial orientation process. Namely, the double bubble tubular film has balanced orientation between and, but the tenter stretched films have higher orientation than. The through-view of the double bubble tubular film shows a uniform diffraction pattern. By contrast, the through-view of the tenter biaxial stretching shows strong diffraction on the meridian direction and the b -axis in the crystalline (molecular chain direction) is prominently oriented in. The simultaneous biaxial stretching has the same trend as the sequential biaxial stretching, but the orientation of the simultaneous biaxial stretching is not as strong as the sequential biaxial stretching..6. Polarized fluorescence observation (molecular orientation in the amorphous region) The polarized fluorescence observation is shown in Figure 8. This result shows the different orientation among biaxial Figure 7 stretching processes. In particular, the double bubble tubular film shows random orientation and the tenter stretching process shows the orthogonal biaxial orientation. From these results, the double bubble tubular film has multiaxis orientation rather than biaxial orientation. The impact strength and shrinkage in hot water are very much influenced by the orientation in the amorphous region. The random orientation gives high impact strength. Further high molecular weight of PA6 for double bubble tubular film makes high impact strength. 4. Conclusion Wide angle X-ray diffraction (WAXD) patterns. In terms of the physical properties of biaxially oriented film, the difference between the double bubble tubular film and

7 M. Takashige and T. Kanai: Physical properties of biaxially oriented PA6 film 7 I II (γ) I (γ) has high impact strength between -5 C and C. This result corresponds to the balanced shrinkage properties. The double bubble tubular film has good balanced properties, particularly the stress-strain curve in tensile property. This property affects high impact strength and good thermoformability. The polarizing fluorescent evaluation result of film orientation in the amorphous portion shows that the double bubble tubular film has uniform orientation on any direction and the tentering process has orthogonal biaxial orientation. Figure 8 I II (γ) Polarized light of fluorescence in-plane. I II (γ) I (γ) I (γ) the tentering process was studied. The simultaneous biaxial and sequential biaxial as film samples of the tenter process was used. Tentering process film has anisotropic tensile properties between and. This result was influenced by later stretching process, namely stretching. In particular, the tensile modulus and tensile strength have opposite properties. The double bubble tubular film has good balanced properties, especially thermal shrinkage and impact strength. Tentering simultaneous has much larger shrinkage in than in. The sequential has larger shrinkage in than in. The double bubble tubular film References [] Kanai T, Takashige M. Seni-gakkaishi 985, 4, 7. [] Takashige M, Kanai T. Int. Polym. Process. 99, 5, 87. [] Kang HJ, White JL. Polym. Eng. Sci. 99,, 8. [4] Kang HJ, White JL, Cakmak M. Int. Polym. Process. 99,, 6. [5] Kang HJ, White JL. Int. Polym. Process. 99, 5, 8. [6] Rhee S, White JL. Int. Polym. Process., 6, 7. [7] Rhee S, White JL. Polym. Eng. Sci. 999, 9, 6. [8] Song K, White JL. Polym. Eng. Sci., 4, 9. [9] Song K, White JL. Int. Polym. Process., 5, 57. [] Song K, White JL. Polym. Eng. Sci., 4,. [] Rhee S, White JL. SPE ANTEC Tech. Papers, 59, 446. [] Rhee S, White JL. SPE ANTEC Tech. Papers, 59,. [] Tobita K, Miki T, Takeuchi N. Film Processing, Kanai T, Campbell G, Eds., Hanser: Munich, 999. [4] Cakmack M. Film Processing, Kanai T, Campbell G, Eds., Hanser: Munich, 999. [5] Tsunashima K, Toyoda K, Yoshii T. Film Processing, Kanai T, Campbell G, Eds., Hanser: Munich, 999. [6] Takashige M. Film Processing, Kanai T, Campbell G, Eds., Hanser: Munich, 999. [7] Yamada T, Nonomura C, Kase S. Film Processing, Kanai T, Campbell G, Eds., Hanser: Munich, 999. [8] Takashige M, Kanai T, Yamada T. Int. Polym. Process. 4, 9, 47. [9] Takashige M, Kanai T, Yamada T. Int. Polym. Process. 4, 9, 47. [] Takashige M, Kanai T. Int. Polym. Process. 5,,. [] Takashige M, Kanai T. Int. Polym. Process. 6,, 86. [] Takashige M, Kanai T. J. Polym. Eng. 8, 8, 79. [] Unitika Japan Patent [4] Toyobo Japan Patent [5] Takashige M, Kanai T, Yamada T. Int. Polym. Process., 8, 68. [6] Takashige M, Kanai T, Yamada T. Int. Polym. Process. 4, 9, 56. [7] Takashige M, Hayashi T. US Patent 5,54,, 996. [8] Takashige M, Hayashi T, Iwamoto T. US Patent 5,76,696, 998. [9] Takashige M, Hayashi T, Iwamoto T. US Patent 6,,5,. [] Uehara H, Sakauchi K, Kanai T, Yamada T. Int. Polym. Process. 4, 9, 55. [] Uehara H, Sakauchi K, Kanai T, Yamada T. Int. Polym. Process. 4, 9, 6. [] Uehara H, Sakauchi K, Kanai T, Yamada T. Int. Polym. Process. 4,9, 7. Q6: Please supply full pp. range, for all references