At present, barrier packaging materials are widely used in food, medicine and other fields. Aluminum foil composites and vacuum aluminum plating materials are often used in barrier packaging. Vacuum aluminum-plating materials instead of aluminum foil composite materials not only reduce production costs, but also reduce the consumption of aluminum materials, so this low-cost and environmentally friendly materials have been unanimously approved by manufacturers and manufacturers.
Vacuum aluminum coating materials can be roughly divided into two categories: vacuum aluminum coating and vacuum aluminum coating. Vacuum aluminum plating films include: VMPET polyester aluminum film, VMCPP cast polypropylene aluminum film, VMBOPP biaxially oriented polypropylene aluminum film, VMCPE polyethylene aluminum film and VMPVC polyvinyl chloride aluminum film. These materials are all formed by coating aluminum on the surface of a polymer film as a substrate. The common characteristic of vacuum aluminum plating materials is that the wear resistance of the aluminum plating layer is poor, so that scratches are easily generated and the dense surface layer is destroyed.
Vacuum aluminized papers and films as barrier materials are usually evaluated for their barrier properties in terms of oxygen transmission rate and water vapor transmission rate. Two different test methods can be used for experiments.
Water vapor transmission rate detection:
Cup method, MOCON moisture permeability tester
According to the GB/T1037-1988 standard, the water vapor transmission rate of the vacuum aluminized film was tested using the cup-type weighing principle. In the process of preparing the sample, the sealing cup is an important step, in this step, the part in contact with the metal seal will inevitably be subject to certain friction and scratches, and the high temperature liquid wax will also Affecting the barrier layer, the sample's water vapor transmission rate will be affected. In addition, the direction of water vapor transmission must also be considered during the experiment. Because the vacuum aluminum plating layer is always exposed on one side of the vacuum aluminized film, when the water vapor passes through the aluminized layer toward the substrate layer, the aluminum plating layer is exposed to a high-humidity environment, and the aluminized layer formed by the adsorption will be formed. Produce pinholes, thereby increasing the amount of water vapor transmission, affecting the use of materials.
According to the standard of ASTM F1249-2001, the water vapor transmission rate test was conducted using a MOCON moisture permeability tester. The specimen is clamped and fixed by the upper and lower chambers, and the fixture will not generate excessive friction on the specimen. The lower chamber of the experimental chamber is filled with distilled water or salt solution, forming a variety of humidity environment, so this method should also pay attention to the direction of water vapor transmission.
According to the experiment, when the water vapor transmission rate test experiment is performed on the vacuum aluminum composite film exposed on the surface of the aluminum-plated layer, the aluminum-plated layer should face the low-humidity environment as much as possible, especially in an environment with a relative humidity of 100%. Even more so, to reduce the impact of water vapor on the denseness of the aluminum plating layer; in experimental methods, according to the ASTM F1249-2001 standard, the use of MOCON moisture permeability tester can be a good way to avoid the impact of experimental operations on experimental data, to obtain samples Test results in the original state.
Oxygen transmission rate detection: differential pressure method, equal pressure method
According to the GB/T1038-2000 standard, the oxygen transmission rate of vacuum aluminized film or paper is tested using the differential pressure principle. The experimental procedure is as follows: Sealing, fixing the sample → Vacuuming the experimental chamber → Filling the upper chamber with oxygen → Continue evacuating the lower chamber → Stop the vacuum and start the test. The vacuum aluminum plating material has poor wear resistance. In this method, when the sample is fixed, the upper and lower chambers of the test chamber are locked by the pressure applied by the clamp. The seal ring will generate a large friction force on the sample, so that The wear resistance of the material deteriorates. In addition, the aluminized layer of the vacuum aluminized film is usually electrostatically adsorbed on the substrate. When the aluminizing layer is faced to the lower chamber during the experiment, the aluminizing layer is affected in the step of vacuuming to reduce the oxygen barrier performance. The vacuum aluminum-plated paper is hard and brittle, and has a large rigidity relative to the film material. The use of the differential pressure test has the disadvantages of poor sealability and easy damage to the aluminum-plated layer when sealed and fixed.
Therefore, when testing the oxygen transmission rate of vacuum aluminum plating materials, it is recommended to use the equal pressure method. According to the ASTM D3985-2002 standard, use the MOCON oxygen permeability tester. On the one hand, on the steps of sealing and fixing the sample, the MOCON oxygen permeability tester has good sealing measures, and the fixing device can avoid repeated friction; on the other hand, this method does not have a vacuum step, so there is no need to worry about the aluminum plating layer. The quality is affected and the oxygen transmission rate can be examined from both sides of the material.
Vacuum aluminum coating materials can be roughly divided into two categories: vacuum aluminum coating and vacuum aluminum coating. Vacuum aluminum plating films include: VMPET polyester aluminum film, VMCPP cast polypropylene aluminum film, VMBOPP biaxially oriented polypropylene aluminum film, VMCPE polyethylene aluminum film and VMPVC polyvinyl chloride aluminum film. These materials are all formed by coating aluminum on the surface of a polymer film as a substrate. The common characteristic of vacuum aluminum plating materials is that the wear resistance of the aluminum plating layer is poor, so that scratches are easily generated and the dense surface layer is destroyed.
Vacuum aluminized papers and films as barrier materials are usually evaluated for their barrier properties in terms of oxygen transmission rate and water vapor transmission rate. Two different test methods can be used for experiments.
Water vapor transmission rate detection:
Cup method, MOCON moisture permeability tester
According to the GB/T1037-1988 standard, the water vapor transmission rate of the vacuum aluminized film was tested using the cup-type weighing principle. In the process of preparing the sample, the sealing cup is an important step, in this step, the part in contact with the metal seal will inevitably be subject to certain friction and scratches, and the high temperature liquid wax will also Affecting the barrier layer, the sample's water vapor transmission rate will be affected. In addition, the direction of water vapor transmission must also be considered during the experiment. Because the vacuum aluminum plating layer is always exposed on one side of the vacuum aluminized film, when the water vapor passes through the aluminized layer toward the substrate layer, the aluminum plating layer is exposed to a high-humidity environment, and the aluminized layer formed by the adsorption will be formed. Produce pinholes, thereby increasing the amount of water vapor transmission, affecting the use of materials.
According to the standard of ASTM F1249-2001, the water vapor transmission rate test was conducted using a MOCON moisture permeability tester. The specimen is clamped and fixed by the upper and lower chambers, and the fixture will not generate excessive friction on the specimen. The lower chamber of the experimental chamber is filled with distilled water or salt solution, forming a variety of humidity environment, so this method should also pay attention to the direction of water vapor transmission.
According to the experiment, when the water vapor transmission rate test experiment is performed on the vacuum aluminum composite film exposed on the surface of the aluminum-plated layer, the aluminum-plated layer should face the low-humidity environment as much as possible, especially in an environment with a relative humidity of 100%. Even more so, to reduce the impact of water vapor on the denseness of the aluminum plating layer; in experimental methods, according to the ASTM F1249-2001 standard, the use of MOCON moisture permeability tester can be a good way to avoid the impact of experimental operations on experimental data, to obtain samples Test results in the original state.
Oxygen transmission rate detection: differential pressure method, equal pressure method
According to the GB/T1038-2000 standard, the oxygen transmission rate of vacuum aluminized film or paper is tested using the differential pressure principle. The experimental procedure is as follows: Sealing, fixing the sample → Vacuuming the experimental chamber → Filling the upper chamber with oxygen → Continue evacuating the lower chamber → Stop the vacuum and start the test. The vacuum aluminum plating material has poor wear resistance. In this method, when the sample is fixed, the upper and lower chambers of the test chamber are locked by the pressure applied by the clamp. The seal ring will generate a large friction force on the sample, so that The wear resistance of the material deteriorates. In addition, the aluminized layer of the vacuum aluminized film is usually electrostatically adsorbed on the substrate. When the aluminizing layer is faced to the lower chamber during the experiment, the aluminizing layer is affected in the step of vacuuming to reduce the oxygen barrier performance. The vacuum aluminum-plated paper is hard and brittle, and has a large rigidity relative to the film material. The use of the differential pressure test has the disadvantages of poor sealability and easy damage to the aluminum-plated layer when sealed and fixed.
Therefore, when testing the oxygen transmission rate of vacuum aluminum plating materials, it is recommended to use the equal pressure method. According to the ASTM D3985-2002 standard, use the MOCON oxygen permeability tester. On the one hand, on the steps of sealing and fixing the sample, the MOCON oxygen permeability tester has good sealing measures, and the fixing device can avoid repeated friction; on the other hand, this method does not have a vacuum step, so there is no need to worry about the aluminum plating layer. The quality is affected and the oxygen transmission rate can be examined from both sides of the material.