Discussion on vacuum packaging of heavy export machinery (2)

Existing problems and solutions

(1) Bottom protection: PVC foamed plastic film is a kind of shock-proof cushioning material, which can be used for 20 days at a rate of 20 grams per square centimeter. It can be packaged directly and is suitable for packing small mechanical products or medicines. For sharp products with large mass and load concentration, they cannot play a role in shock-proof buffering. Therefore, there is a characteristic of lost packaging materials as the bottom layer protection, and the price of the PVC bubble film is relatively high, which increases the packaging cost. Therefore, it is possible to select a material that is relatively inexpensive and can serve as a barrier to isolation, such as ordinary fiber materials.

(2) Mechanical fixing: The fixing of the machine is to fix the base of the machine to the wooden sleeper. In the currently used operation method, the screw of the fixing mechanism penetrates the composite material, so that the sealing property of the composite material is damaged. To ensure that the seal is not damaged on the basis of mechanical fixation, we can add a layer of rubber gasket between layers l and 2 to prevent the metal surface of the silicon surface from scratching the composite material, and the rubber gasket must be elastic. Large, non-aged rubber can prevent more effectively the air leakage of the screw perforation. If necessary, apply a layer of sealant around the screw, or choose a new type of packaging material such as heat-shrinkable material to reduce the permeability of the perforation.

(3) Sealability of vacuum packaging: The sealing performance of composite flexible packaging directly affects the quality of the packaging and the shelf life of the packaged products. Therefore, the sealing performance of composite materials is required to achieve the best state. The evaluation of the sealing performance has three parameters: heat sealing strength, sealability of the sealing interface, and hot tack strength.

Sealing performance evaluation

(1) Heat seal strength

The heat seal strength refers to the energy consumed for peeling the heat seal interface of a standard sample under constant temperature and humidity conditions. The value reflects the highest withstand voltage capability that can be achieved at the sealing area of ​​the film. Heat seal strength formula:

B = peak value of the force applied to the material F(N)/width of the specimen b (cm)

The greater the value of the heat seal strength, the better the heat seal effect, that is, the greater the peak force of the material, the better the heat seal effect. The best seal is that the strength of the seal is equivalent to the strength of the sealed body film. Samples can be taken for tensile testing at the heat seal and checked for strength values ​​and breakage locations. If cracking occurs in the bulk material and the body breaks, it is mainly near the seal where the material has become thinner, such seal is acceptable; if it breaks in the seal area, the seal is weak point.

(2) sealing interface sealability

The sealability of the sealing interface refers to the ability to withstand the erosion, penetration, and diffusion of the contents of the package caused by the degree of compaction of the heat-seal interface, and is essentially a durability index of the heat-sealing performance, and the heat-seal strength is the basis thereof.

(3) Hot bond strength

The hot tack strength is used to characterize the heat seal strength of the film before it is cooled in the seal, that is, in a semi-molten state. Hot tack strength is an important factor limiting the packaging speed of vertical automatic packaging machines. When using a small hand-held heat sealer for sealing, the hot-tack strength has little effect on the sealing effect.

(to be continued)