Article Summary
Plastic composite film is a multi-layer plastic film formed by compounding or extruding two or more different plastic films. Composite films have comprehensive properties of various individual materials and have been widely used in food packaging due to their excellent heat sealing properties. Heat sealing strength is one of the important physical indicators of food packaging. Excessive or insufficient heat sealing strength can cause abnormal phenomena such as packaging leakage and damage. The commonly used materials for food flexible packaging include polyethylene (PE polyethylene), biaxially oriented polypropylene (BOPP), cast polypropylene (CPP cast polypropylene), vacuum aluminum coated polyester (VMCPP vacuum aluminum cast polypropylene), polyester (PET polyester), vacuum aluminum coated polyester (VMPET vacuum aluminum coated polyester), aluminum foil (AL aluminum), etc. Xu Wenda et al. explained the packaging performance of the above materials and the composite method of composite flexible packaging [3]. Wang Dongsheng [4] studied the factors affecting the heat sealing quality of PET/PE composite films, compared and analyzed the effects of heat sealing direction, temperature, and speed on heat sealing quality, and summarized the optimal heat sealing process parameters for PET/PE composite films. Zhao Manman and others
[5] The effects of heat sealing temperature, time, and pressure on the heat sealing strength of PET/AL/PE composite films were studied, and the effective heat sealing temperature range of PET/AL/PE composite films was determined. Sun Zhihui et al. [6] studied the heat sealing parameters and strength of polyethylene materials, and found that the thickness of plastic film, heat sealing temperature, time, and pressure all have an impact on the heat sealing strength, with the heat sealing temperature having the most significant effect on the heat sealing strength.
BOPP/VMPET/CPP and PET/VMPET/CPP materials both have good barrier properties, good printing effects, safety and hygiene, as well as good heat sealing performance and high strength, making them easy for automation and high-speed production. Thus, it is widely used in food packaging. In the packaging process of food factories, when switching between BOPP/VMPET/CPP and PET/VMPET/CPP composite films on the same packaging machine, if the equipment parameters are not adjusted properly, the problem of unstable heat sealing quality may occur. Under the same heat sealing pressure and time, this experiment used different heat sealing temperatures to seal two types of composite films, and tested and evaluated the heat sealing strength and sealing performance.
experiment
1.1 Materials
BOPP， Thickness 19 μ m, Wenzhou Jintian Plastic Industry Co., Ltd; PET， Thickness 12 μ m, VMPET, Thickness 12 μ m, Zhejiang Changyu New Materials Co., Ltd; CPP， Thickness 30 μ m, Shishi Yanying Plastic Co., Ltd; One component water-based adhesive, Dow Chemical China Co., Ltd; Solvent based polyurethane adhesive, Beijing Gaomeng New Materials Co., Ltd.
1.2 Equipment and Instruments
Dry laminating machine (DL250), Shaanxi Beiren Printing Machinery Co., Ltd; Vertical packaging machine (RL420), Shanghai Ruiji Jinhong Packaging Machinery Co., Ltd; Tensile testing machine (GBH-1), sealing testing instrument (GB-M), Guangzhou Biaoji Packaging Equipment Co., Ltd.
1.3 Method
1.3.1 Composite film synthesis
Composite BOPP19, PET12, VMPET12, and CPP30 single materials in a dry laminating machine to form composite materials with a three-layer structure of BOPP12/VMPET12/CPP30 and PET12/VMPET12/CPP30, respectively. Among them, BOPP19/VMPET12 layer and PET12/VMPET12 layer are composed of single component water gel composite. VMPET12/CPP30 is compounded with solvent based polyurethane adhesive. After curing at 45 ℃ for 36 hours in a curing chamber, the two composite materials were divided into rolls with a width of 210mm.
1.3.2 Composite film packaging
Two types of composite films are packaged on the same vertical packaging machine, with a longitudinal sealing width of 15mm and a transverse sealing width of 10mm. The sealing pressure is 0.3MPa, the longitudinal sealing time is 0.38 seconds, the transverse sealing time is 0.4 seconds, and the longitudinal sealing temperature is 137 ℃ (the best longitudinal sealing temperature obtained through long-term experimental verification). The transverse sealing temperature is set within the range of 169 ℃ -197 ℃, with each group consisting of 4 ℃. Each group produces 50 packaging bags, with each group consisting of 10 bags as a sampling section, for a total of 5 sampling sections.
1.3.3 Heat sealing strength test
Samples will be taken from the produced packaging bags, with 2 bags randomly sampled from each sampling section. A total of 10 bags will be sampled from each group (Table 1). According to the test method for heat sealing strength of plastic film packaging bags (QB/T2358-1998), the heat sealing performance of the packaging bags will be tested using a tensile testing machine (GBH-1). To improve the accuracy of the test results, each packaging bag was measured at three positions: upper horizontal seal, lower horizontal seal, and vertical seal. The sampling width was 15mm, and the sampling unfolded length was 100mm. During the testing process, the sample was opened 180 degrees from the heat sealed area, and the two ends of the sample were clamped on the two fixtures of the testing machine with a distance of 50mm between the fixtures. The testing speed was 300mm/minute, and the maximum load at fracture was read.
TH=Tear at heat seal/film width; TH - Heat sealing strength (KN/m)
1.3.4 Sealing test
Samples will be taken from the produced packaging bags, with 2 bags randomly sampled from each sampling section. A total of 10 bags will be sampled from each group (Table 1). The sealed performance of the packaging bags will be tested using a sealing tester (GB-M) according to the sealing performance test method for flexible packaging (GB/T15171-1994). To improve the accuracy of the test results, the longitudinal seal of the packaging bag was folded in advance before testing. During the testing process, the test sample was laid flat and completely covered by the pressure plate. After the sample was placed, the horizontal plane exceeded the pressure plate by more than 25mm (Figure 1). Detect pressure of -0.6bar for 30 seconds.
Figure 1 Sealing type test
2 Analysis and Discussion
2.1 Heat sealing strength test
Longitudinal sealing heat sealing strength: Take the average heat sealing strength of two packages in each section. According to Figure 2, the longitudinal sealing heat sealing strength of BOPP19/VMPET12/CPP30 is between 24.1N/15mm-24.6N/15mm, and the longitudinal sealing heat sealing strength of PET12/VMPET12/CPP30 is between 23.4N/15mm-24.1N/15mm. From this, it can be seen that when the longitudinal sealing temperature is set at 137 ℃, the longitudinal sealing heat sealing strength of BOPP19/VMPET12/CPP30 is slightly higher than that of PET12/VMPET12/CPP30. The peel strength of the two materials tends to stabilize, and the difference in heat sealing strength between the two materials is not significant.
Horizontal heat sealing strength: The value rule for horizontal heat sealing strength is 10 packaging bags per group, and the average heat sealing strength is taken. According to Figure 3, as the temperature increases, the horizontal heat sealing strength of the two composite materials gradually increases first, and when a certain temperature is reached, the horizontal heat sealing strength gradually decreases. When the transverse sealing temperature is in the range of 169 ℃ -173 ℃, the transverse heat sealing strength of BOPP19/VMPET12/CPP30 material is between 20.21N/15mm and 21.32N/15mm, and the transverse heat sealing strength of PET12/VMPET12/CPP30 material is between 23.33N/15mm and 23.55N/15mm. The transverse heat sealing strength of BOPP19/VMPET12/CPP30 material is lower than that of PET12/VMPET12/CPP30 material. When the transverse sealing temperature is in the range of 177 ℃ -189 ℃, the transverse heat sealing strength of BOPP19/VMPET12/CPP30 material is between 24.33N/15mm-26.88N/15mm, and the transverse heat sealing strength of PET12/VMPET12/CPP30 material is between 23.10N/15mm-25.39N/15mm. The transverse heat sealing strength of BOPP19/VMPET12/CPP30 material is higher than that of PET12/VMPET12/CPP30 material. When the transverse sealing temperature is in the range of 193 ℃ -197 ℃, the transverse heat sealing strength of BOPP19/VMPET12/CPP30 material is between 25.65N/15mm and 24.32N/15mm, and the transverse heat sealing strength of PET12/VMPET12/CPP30 material is between 25.88N/15mm and 25.44N/15mm. The transverse heat sealing strength of BOPP19/VMPET12/CPP30 material returns to being lower than that of PET12/VMPET12/CPP30 material.
2.2 Sealing test
The sampling rule for the sealed test is 10 packaging bags per group, and the sealing test is conducted on each packaging bag. According to Table 2, when the horizontal sealing temperature is 169 ℃, all 10 bags of BOPP19/VMPET12/CPP30 material packaging bags leak air, with a leakage rate of 100%; When the horizontal sealing temperature is 173 ℃, 5 bags of BOPP19/VMPET12/CPP30 material packaging have air leakage, with a leakage rate of 50%; When the horizontal sealing temperature is between 177 ℃ and 185 ℃, the BOPP19/VMPET12/CPP30 material packaging bag does not leak air, with a leakage rate of 0%; When the horizontal sealing temperature is 189 ℃, there are 6 packages of BOPP19/VMPET12/CPP30 material packaging bags leaking air, with a leakage rate of 60%; When the horizontal sealing temperature is 193 ℃, there are 8 packages of BOPP19/VMPET12/CPP30 material packaging bags leaking air, with a leakage rate of 80%; When the horizontal sealing temperature is 197 ℃, all 10 bags of BOPP19/VMPET12/CPP30 material packaging bags leak air, with a leakage rate of 100%. According to Table 3, when the horizontal sealing temperature is 169 ℃, 6 packages of PET12/VMPET12/CPP30 material packaging bags leak air, with a leakage rate of 60%; When the horizontal sealing temperature is between 173 ℃ and 193 ℃, the PET12/VMPET12/CPP30 material packaging bag does not leak air, with a leakage rate of 0%; When the horizontal sealing temperature is 197 ℃, 4 packages of PET12/VMPET12/CPP30 material packaging bags leak air, with a leakage rate of 40%.
In summary, when the transverse sealing temperature is lower than the optimal transverse sealing temperature range, the fusion joint of the T-shaped heat sealing layer may leak due to incomplete fusion, resulting in air leakage. When the transverse sealing temperature is lower than the optimal transverse sealing temperature range, the fusion joint of the T-mouth heat sealing layer may melt or have pinholes due to excessive fusion, resulting in air leakage.
When the horizontal sealing temperature is between 177 ℃ and 185 ℃, the air leakage rate of BOPP19/VMPET12/CPP30 material packaging bags is 0%, and the optimal horizontal sealing temperature range for this material is 181 ℃± 4 ℃. When the horizontal sealing temperature is between 173 ℃ and 193 ℃, the leakage rate of PET12/VMPET12/CPP30 material packaging bags is 0%. The optimal horizontal sealing temperature range for this material is 183 ℃± 10 ℃.
conclusion
The heat sealing strength and sealing performance of composite films are affected by heat sealing time, heat sealing pressure, and heat sealing temperature. During the packaging process of a vertical packaging machine, a longitudinal heat sealer is first used to longitudinally heat seal the film at the interface of the rolled cylinder to obtain a sealed tube. Then, the cylindrical film is moved to the position of the transverse heat sealer for transverse sealing, forming a packaging bag cylinder. Then heat seal with a horizontal heat sealer and cut in the center to form a packaging bag unit, while forming the bottom seal of the next cylindrical bag. So when the heat sealing time and pressure are fixed, the heat sealing temperature has a more significant impact on the heat sealing strength and sealing performance.
According to multiple repeated experiments, it has been proven that the optimal transverse sealing temperature for packaging BOPP19/VMPET12/CPP30 materials using a vertical packaging machine is 177 ℃ -185 ℃, and the optimal transverse sealing temperature for packaging PET12/VMPET12/CPP30 materials is 173 ℃ -193 ℃. The optimal horizontal sealing temperature range for BOPP19/VMPET12/CPP30 is relatively small. When switching between BOPP/VMPET/CPP and PET/VMPET/CPP materials on the same packaging machine, it is important to pay attention to the characteristics of the two materials and select the optimal horizontal sealing temperature range for production. Especially when switching from PET12/VMPET12/CPP30 material to BOPP19/VMPET12/CPP30 material, it is necessary to reset the heat sealing temperature suitable for BOPP/VMPET/CPP material for production to reduce quality hazards.
This experiment mainly explored the influence of heat sealing temperature on the heat sealing strength and sealing performance of composite films. The effects of heat sealing pressure and time on the heat sealing strength and sealing performance of composite films were not thoroughly studied. Further improvement and tracking testing will be conducted in the subsequent production and experimental processes.
Editor:Sichuan Jinzhongde Science and Technology Research Institute
Source: China Packaging Federation Plastic Packaging Committee China Packaging Federation Plastic Packaging Professional Committee
