Detection And Importance Of The Tightness Of Plastic Cap

Update:08 Apr 2019

The plastic cap are only part of the sealed container, […]

The plastic cap are only part of the sealed container, however, its sealing performance is very important. Here we analyze the reason and importance of the sealing performance of the cap. The barrier properties of standard packaging materials will directly affect the shelf life of the product. Generally speaking, the better the barrier performance of the container, the longer the shelf life of the contents, but the sealing performance of the container is the premise to achieve its barrier performance. Only the container has a good sealing performance to ensure the effectiveness of the barrier material. Regardless of the barrier properties of the bottle caps, the connection between the bottle and the cap, that is, the connection between the bottle thread and the cap, is also the position where the container may leak. This position is within the detection range of the cap sealing performance. The sealing performance of the cap basically reflects the sealing performance of the container and is one of the necessary inspection items for the cap.

The lack of material in the plastic bottle cap refers to a partial incomplete phenomenon at the end of the stream or a part of the multi-cavity is not completely filled, generally occurring at a position away from or thin section. The filling pressure and speed is too slow. During the injection molding process, the pressure in the cavity is insufficient due to pressure loss, and it is difficult for the melt to fill the entire cavity. The injection time is too short, the melt has not filled the cavity, and the injection process has ended. The injection time can be extended or the injection speed can be increased. The mold temperature is too low, the flow resistance of the melt increases, the flow rate is slowed down, and even in the middle of the flow path, gate or filling, the solid material is prevented from continuing to feed, and the cavity is not easily filled. The temperature of the chiller can be increased to increase the mold temperature. The temperature of the tube or the temperature of the hot runner is too low, which affects the fluidity of the melt, which may easily lead to insufficient filling, and may appropriately increase the temperature or increase the injection pressure.

The sealing principle and sealing structure of the two types of caps are different: the single-piece cover is sealed by the sealing ring, the top seals and the side seal to ensure the sealing effect, wherein the sealing ring is necessary, and the side seal and the top seal are sealed according to the seal. The effect requirements and the design requirements of the cap structure can be selected. Through the three structures of the seal ring, top seal and side seal, the inner and outer contact passages of the bottle are isolated from the inside, the top and the outside of the bottle mouth. If the thread needs to be sealed, the contents can fill the thread gap between the cap and the mouth of the bottle, and no longer leak out.

When the cap is tightened, the thread on the cap conforms to the thread on the bottle, and as the rotation progresses, the thread of the cap pushes down continuously. Notice that there is a ring-shaped protrusion that is not threaded at the bottom of the thread on the bottle. This is the lowest position that the thread of the cover can reach. When the cover is pushed down continuously because of the rotation, it will be blocked by the protruding ring, and the thread at the lower end of the cover will be stuck at the bottom of the bottle and this Between the "rings", because of the labor-saving effect of the bevel, we can continue to screw the cover relatively easily, so the thread of the plastic data has been deformed, and there is a backlog between them. There is a momentum that wants to push the cover in the opposite direction, but because of the cover. The friction between the thread and the thread of the bottle is proportional to the pressure in the kneading between the two threads, thus preventing the cap from actually rotating around the opposite direction.

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