Easy Tear Multilayer Film of Biaxially Oriented PA6/MXD6 by Double Bubble Tubular Film Process

Transcription

1 REGULAR CONTRIBUTED ARTICLES M. Takashige 1 *, T. Kanai 2 1 Idemitsu Unitech Co., Hyogo, Japan 2 Idemitsu Kosan Co., Chiba, Japan Easy Tear Multilayer Film of Biaxially Oriented / by Double Bubble Tubular Film Process In the market, a film which is adapted to environmental and barrier problems and easy tear property is desired. A previous report discussed easy tear film. This report discusses the film having not only easy tear, but also high barrier properties. A biaxially oriented / blend film produced by double bubble tubular film process does possess gas barrier. So a multilayer film having high gas barrier layer and keeping easy tear cut has been studied. High gas barrier layer of high content MXD 6 in the center layer is added to / blend film in the outer layers. When blending ratio of / blending film layer is, the property of easy straight line cut is obtained. It is found that the plate-like cylinder structure was formed in the observation of TEM for / blend film. The multilayer biaxially oriented film composed of / blend layer and high content layer keeps high strength, easy tear property and high gas barrier. Namely, the material and production technology of a film could solve environmental and barrier problems. 1 Introduction In recent years, environmental problems have come into question in the packaging industry. These problems, the de-chlorination and waste reduction, have brought concerns in this industry, especially waste reduction which has been a serious problem. It is our desire that the waste reduction problem is solved. In order to achieve this waste reduction, there is a rapid increasing shift from a bottle to a standing pouch for repackaging use in an effort to utilize resources effectively. For the provision of this standing repackage pouch, thin and strong biaxially oriented film is indispensable. film has inferior oxygen gas barrier performance. K coated film, which coats the surface of biaxial stretching film with polyvinylidene chloride in order to raise the oxygen gas barrier performance until now, was used. When this film * Mail address: M. Takashige, Idemitsu Unitech Co., Ltd., Kou, Shirahama-cho, Himeji-City, Hyogo, Japan masao.takashige@iut.idemitsu.co.jp is incinerated, it generates toxic gas such as chlorine gas and dioxins. The development of oxygen gas barrier film without K coated layer is desired. A previous report discussed an oxygen gas barrier / blend film which satisfies formability and physical property using blending technology. As a gas barrier resin, poly (m-xylene adipamide) () was selected. Moreover higher gas barrier properties which have the same level as K coated film is sometimes required. The patent describes PA 6 and multi-layered film [1, 2], but property of easy straight line cut is not available. The bag is simple and safe to open, for children and even for elderly people. In the medical field, there are many applications, where we cannot use a pair of scissors for safety and hygiene reason, so the development of a film with the easy open access is desired. The development of the film with compatible performance of toughness, opening-ability and high barrier is the goal. Polymer blends are a useful method in order to obtain the new material from existing material [3 to 6]. The research on blending between and other resins has been made. It has been explained that mixed and stretched resin and resin at the fixed compounding ratio can make a film with easier tear property in the patent [7]. It was found that blending film has the straight line cut as a new property. Blending samples of and has been studied by changing the melting condition by Takeda [8 to 10]. It is known that this system involves reactive blending from research in the past. Shibayama has made a reaction analysis of and [11, 12]. There are several reports issued on double bubble tubular stretching technology [13 to 24] of formability and structure analysis for resin such as PET, PBT, PPS, -12 and PA12 that are reported by White, Kang, Song, Rhee et al. [15 to 24]. However, there are no reports on double bubble tubular technology of the multilayer film. The analyses of deformation behavior of were reported previously according to stretching stress analyses [25]. The previous report discussed easy tear film [26]. This study was carried out to clarify the relationship among multilayer composition, gas barrier property and stretched film structure. It should aim at the development of a barrier film with open-easiness and straight line cut keeping the toughness of biaxial stretching film. 100 Hanser Publishers, Munich Intern. Polymer Processing XX (2005) 1

2 Fig. 1. Schematic view of double bubble tubular process (multilayer process) a: extruder (EX1, EX2, EX3), b: die (3 layers), c: cooling bath, d: take up roll, e: air ring, f: heating furnace, g: annealing, h: winding 2 Experimental 2.1 Equipment Apparatus used for the double bubble tubular film process is shown in Fig. 1. By using three extruders namely an 40 mm extruder (L/D = 24), an 40 mm extruder (L/D = 25) as outer layers and an 40 mm extruder (L/D = 25) as a center layer with a three layer circular die of the diameter of 75 mm and the lip clearance of 1 mm and with a water-cooling ring having the diameter of 90 mm. While passing 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 heatset using a heat treatment device. 2.2 Material The material was Ube PA 1023FD (PA 6) with mean molecular weight of and the relative viscosity of g r = 3.5 in 98 % sulfuric acid as a solvent. The material was Mitsubishi Gas Chemical MX PA 6007 with mean molecular weight of and the relative viscosity of g r = 2.7 in 96 % sulfuric acid as a solvent. The center layer is changed by the ratio of and shown in Fig. 2. Fig. 2. Image of multilayer structure 2.3 Experimental Method The melt process conditions of the non-stretched film were 270 C for resin temperature at the die exit, 1.2 for blow up ratio, and 6.0 for draw down ratio respectively. Three layer thickness ratio is 1/1/1 for outer layer/center layer/outer layer shown in Table 1. The center layer is changed MXD, /MXD 30/70, /MXD 70/30 and. -MXD blend for outer layer is 70/30 which is best composition for easy tear and thickness uniformity obtained from the previous report [26]. The extrusion rate was 17.6 kg/h and the take up velocity was 6.4 m/min. Film was quenched in water at 20 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 45, was installed at the upper part of the heating furnace. The standard condition for stretching process was set at 330 C for process temperature (temperature of heating furnace) and MD (Machine Direction)/TD (Transverse Direction) = 3.5/3.5 for stretching ratio respectively. 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 our previous papers. The stretching stress was calculated with the help of the tubular theoretical equation reported by the authors et al. [25]. The maximum stress at the end point of stretching may 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. Intern. Polymer Processing XX (2005) 1 101

3 Properties Case-1 Case-2 Case-3 Case-4 3 layers structure Outside layer Center layer 2.4 Observation of TEM Phosphorus wolframic acid was used to dye the film. A thin section was cut down using the microtome. The phase separation structure was evaluated by the electron microscopy (TEM; Nihon Denshi JEM-200CX). The film of the blending ratio of the / 70/30 resin was used. Edge view and end view were selected as a measurement direction. 2.5 Mechanical Properties An evaluation of gas barrier and toughness was also carried out. The oxygen gas permeability was carried out under 23 C, 60 % RH condition by using Mocon Oxtran. The toughness was evaluated by using the film impact strength equipment with 1/2 inch ball produced by Toyo Seiki. The tearing resistance was evaluated by using the elemendorf tearing test machine. The straight line cut was evaluated by using the stretched film sample. The film was torn 200 mm length, and the deviation length was measured. 3 Results and Discussion Inside layer The influence of multilayer composition and MXD 6 blend ratio on stretchability, stretching stress and physical properties of biaxially oriented film including gas permeability and easy straight line cut is studied by using the double bubble tubular multilayer film machine. The outer layers are composed of / = 70/30 and center layer is high content layer as a gas barrier layer shown in Fig. 2. Processability Good Good Good Good Stretching stress TD (MPa) Straight line cut (Deviation) MD 2~6 0~2 0~2 0~4 (mm) Elemendorf tearing resistance MD (N/cm) Film impact strength (J/m) Table1. Physical properties of biaxially oriented / multilayer film (outside/center/inside = 1/1/1) 3.1 Multilayer Structure and Processability of Biaxial Orientation The results of stretchability, stretching stress, physical properties such as impact strength, gas barrier and easy straight line cut for various multilayer film including / blend layers are shown in Fig. 1. All resins have good processability and continuous processing is possible without any break because of using. Fig. 3. Relationship between process temperature and stretching stress 102 Intern. Polymer Processing XX (2005) 1

4 3.2 Stretchability The results of stretching stress obtained by changing the set temperature of heating furnace are shown in Fig. 3. The stretching stress decreases with increasing stretching temperature. It is found that blend resin shows higher temperature dependence of stretching stress than. As a result, stretching process window of blend resin is narrower than one of. As the ratio of to / blend increases, the stretching stress decreases, because the hydrogen bonding of is suppressed by the steric hindrance of. 3.3 Impact Strength Fig. 4 shows that the impact strength increases with increasing stretching stress. The impact strength is proportional to stretching stress. From this result, film impact can maintain J/m by keeping over stretching stress 70 MPa. blend film which has lower impact strength than film can have high impact strength by achieving high stretching ratio. 3.4 Oxygen Gas Permeability Oxygen gas permeability of multi-layer film is changed by the blend ratio of as a center layer. As shown in Fig. 5, oxygen gas permeability decreases with increasing the ratio of. If the permeability is less than 7 cm 3 /m 2 day, the ratio of is required over 45 %. If this condition is satisfied, the oxygen gas permeability of this film is more excellent than the one of K-coated film targeted. 3.5 Easy Tear Property The influence of the blend ratio on easy tear property is shown in Table 1. The tear strength of film decreases with increasing the content of and no anisotropy between MD and TD is observed. Easy straight line cut property is only MD direction which is also observed in the previous report [26]. Fig. 4. Relationship between stretching stress and film impact strength Fig. 5. Relationship between contents and oxygen gas permeability Properties Sample Case-1 Case-2 Case-3 Straight line cut (Deviation) The easy straight line cut in TD is not obtained even by increasing ratio of. Easy tear and easy straight line cut property is achieved even in case of for center layer if the multilayer film has both the outer layers maintaining / 70/30. But the multilayered film having in the center layer has worse straight line cut property and higher tear resistance. As the physical properties of the single layer are shown in Table 2, has lower tear strength and easier straight line cut than. Further, the blend polymer of / 70/30 in the outer layers gives easier tear property than. The blend ratio of / 30/70 in the center layer gives much easier straight line cut property than. 3.6 TEM Observation of Three Layer Film In order to know the mechanism of easy straight line cut, the morphology of non-stretched multilayer film is studied by using TEM. The TEM photo of Fig. 6 shows the cylindrical structure of MDX6 in the matrix is observed in the both outer layers. This cylinder structure is elongated along the MD direction even for multilayer and non-stretched film. It is confirmed that easy straight line cut is due to the cylindrical structure. Intern. Polymer Processing XX (2005) Resin MD (mm) / = 70/ (Blending) 30 ~ ~ 20 0 ~ 2 Tearing resistance (N/cm) Table 2. Physical properties of biaxially oriented and single layer film

5 Fig. 6. Observation of TEM of a 3 layer structure From the results of multilayer film, the outer layers of / MDX6 = 70/30 has both easy straight line cut and high impact strength. In case of rich blend in the center layer, TEM observation shown in Fig. 7 shows matrix domain structure is opposite pattern, namely is matrix and is cylindrical structure. rich blend film has more excellent easy straight line cut and easier tear than. In the previous report [26], non-stretched film already has cylindrical structure and when film stretched in both MD and TD it has more excellent easy straight line cut property. The technological combination of / blend and multilayer including barrier layer can produce high performance film having easy tear, high barrier and high mechanical property which are usually difficult to be achieved. Namely, the material and production technology of a film could solve environmental and barrier free problems. The bag is simple and safe to open, for children and even for elderly people. In the medical field, there are many applications, where we cannot use a pair of scissors for safety and hygiene reason, so the development of a film with the easy open access is desired. 4 Conclusion It was confirmed that blending layer blended in the outer layers has the straight line cut in MD and rich layer in the center layer has high barrier performance. It is found that the plate-like cylinder structure was formed even in a non-stretched film from observations of TEM. The cylinder structure produced the straight line cut. A high strength film was achieved, because it was stretched biaxially using the double bubble tubular process. The multilayer double bubble tubular film composed of blending materials and maintain the compatible performance of high strength, easy tear property and high barrier and it could solve environmental and barrier free problems. Fig. 7. Observation of TEM of a 3 layer structure References 1 Japan Patent S (1982) 2 Japan Patent H (1992) 3 Nishi, T., Wang, T. T.: Macromolecules. 8, p. 909 (1975) 4 Chuang, H. K, Han, C. D.: J. Appl. Polym. Sci. 30, p. 165 (1985) 5 Greco, R., Malincoico, M.: Polymer 29, p (1988) 6 Jo, W. H., Kim, G., Chae, S. H.: Polymer Journal 25, p (1993) 7 U.S. Patent (1996) Takashige, M., Hayashi, T. 8 Takeda, Y., Paul, D, R.: Polymer 33, p. 899 (1992) 9 Takeda, Y., Keskkula, H., Paul, D. R.: Polymer 33, p (1992) 10 Takeda, Y. Paul, D. R.: Polymer. 32, p (1991) 11 Shibayama, M., Uenoyama, K., Oura, J., Iwamoto, T.: Polymer 36, p (1995) 12 Shibayama, M., Oura, J., Iwamoto, T.: Kobunshi Ronbunsyu. 53, p. 453 (1996) 13 Kanai, T., Takashige, M.: Seni-Gakkaishi 41, p. 272 (1985) 14 Takashige, M.: Film Processing, in: Kanai, T., Campbell, G. Eds., Progress in Polymer Processing Series. Hanser, Munich (1999) 15 Kang, H. J., White, J. L.: Polym. Eng. Sci. 30, p (1990) 16 Kang, H. J., White, J. L., Cakmak, M.: Int. Polym. Process. 1, p. 62 (1990) 17 Kang, H. J., White, J. L.: Int. Polym. Process. 5, p. 38 (1990) 18 Rhee, S., White, J. L.: Int. Polym. Process. 16, p. 272 (2001) 19 Rhee, S., White, J. L.: Polym. Eng. Sci. 39, p (1999) 20 Song, K., White, J. L.: Polym. Eng. Sci. 40, p. 902 (2000) 21 Song, K., White, J. L.: Int. Polym. Process. 15, p. 157 (2000) 22 Song, K., White, J. L.: Polym. Eng. Sci. 40, p (2000) 23 Rhee, S., White, J. L.: SPE ANTEC Tech. Papers. 59, p (2001) 24 Rhee, S., White, J. L.: SPE ANTEC Tech. Papers. 59, p (2001) 25 Takashige, M., Kanai, T.: Int. Polym. Process. 5, p. 287 (1990) 26 Takashige, M., Kanai, T., Yamada., T.: Int. Polym. Process. 19, p. 147 (2004) Date received: November 7, 2004 Date accepted: January 4, Intern. Polymer Processing XX (2005) 1