Sealing principle between bottle cap and bottle mouth

Cosmetic packaging materials, whether glass bottles, plastic containers such as PET bottles, acrylic bottles, or tubes, need to be taken out through removal tools such as bottle caps or pump heads. If the safety of the inner materials can be guaranteed without leakage, the seal between the bottle cap and the container is very critical.

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Basic knowledge of sealing

?1. Bottle cap and bottle mouth

The bottle cap and bottle mouth meet the following requirements through a certain connection and cooperation form:

a. The bottle cap is fixed on the bottle mouth through the connection between the bottle cap and the bottle mouth, and can be opened or closed in a certain way;

b. Provide sufficient pressure on the sealing contact surface, and the pressure should be evenly distributed. The pressure should be maintained constant before the container is opened or for a longer period of time;

c. For the bottle cap structure without liner, the sealing part contacting with the bottle mouth should be smooth, uniform and in good contact;

d. Opening and closing is easy, quick and leak-free.

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2. Bottle cap and sealing liner?

In order to accurately press the sealing liner against the sealing contact surface, the sealing liner should be accurately positioned in the bottle cap and have an appropriate size.

3. Seal the liner and bottle mouth?

The matching design between the sealing liner and the bottle mouth needs to determine the contact mode, contact area, contact width and thickness of the sealing liner to ensure sufficient elasticity and necessary rigidity requirements.?

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Sealing principle

The purpose is to set up a perfect physical barrier at the bottle mouth where leakage (gas or liquid contents) or intrusion (air, water vapor or impurities in the external environment, etc.) may occur and the bottle mouth needs to be sealed. To achieve this goal, the lining must be elastic enough to fill any unevenness on the sealing surface, while maintaining sufficient rigidity to prevent squeezing into the surface gap under the sealing pressure. Both elasticity and rigidity must be constant.?

To achieve a good sealing effect, the liner pressed against the bottle mouth sealing surface must maintain a sufficient pressure during the shelf life of the package. Within a reasonable range, the higher the pressure, the better the sealing effect. However, it is obvious that when the pressure increases to a certain level, it will cause the bottle cap to break or deform, the glass bottle mouth to break or the plastic container to deform, and the liner to be damaged, causing the seal to fail.?The sealing pressure ensures good contact between the liner and the bottle mouth sealing surface. The larger the bottle mouth sealing area, the larger the area distribution of the load applied by the bottle cap, and the worse the sealing effect under a certain torque. Therefore, in order to obtain a good seal, it is not necessary to use too high a fixing torque. The width of the sealing surface should be as small as possible without damaging the liner and its surface. In other words, if a small fixing torque is to achieve the maximum effective sealing pressure, a narrow sealing ring should be used.

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Conventional sealing methods

?1. Thread engagement

Thread engagement refers to the number of turns from the first engagement point between the starting point of the screw cap's thread and the starting point of the bottle mouth's thread to the point where the bottle mouth's sealing surface contacts the liner. In order for the liner to be evenly pressed against the entire circumference of the bottle mouth's sealing surface, at least one full turn of thread engagement is required. The larger the area of thread engagement, the better the positioning of the bottle cap, and the greater the effect of the fixing torque that keeps the bottle cap in place. The pitch determines the inclination or slope of the thread. The larger the pitch, the greater the thread slope, the faster the bottle cap can be screwed on or off, and the greater the height of the bottle cap required to achieve a certain number of turns of thread engagement. Therefore, it is best to have an appropriate pitch. There is no need to choose a pitch that is too large, so as not to affect the beauty of the shape and increase production costs.

?2. Fixing torque

Once the cap and bottle mouth structure are determined, the requirement for a good seal is easy to solve. The problem comes down to whether the cap can apply appropriate pressure to the bottle mouth. For screw caps, a scale is needed to measure the effect of the cap - the fixing torque. The fixing torque can be measured by a torque tester. In practice, since the torque tester cannot be placed under the capping machine head, it must be measured by the " loosening torque " applied by the tester to the bottle cap . The fixing torque changes with the diameter of the bottle cap in direct proportion. The reliability of the cap seal depends on the elasticity of the liner, the flatness of the sealing surface, etc., not just its tightness or the torque applied.?

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Other types of bottle cap seal reference

?1. Sealing the edge of the bottle

The sealing surface of the bottle mouth rim seal is on the upper outer edge of the bottle mouth. The natural or synthetic rubber gasket is placed on the edge of the metal lug cover. The edge of the bottle mouth is consistent with the tapered sealing surface on the upper part of the outer edge of the bottle mouth. The seal is mainly achieved by the pressure exerted by the flange of the bottle mouth.

?2. Joint seal

Combined sealing is a double seal between the sealing surface on the bottle mouth and the sealing surface on the edge of the bottle mouth. The technical requirements for combined sealing are relatively high.?

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3. Plug sealing

The plug seal is formed by the friction between the plugs made of various materials and the inner edge of the plug-shaped bottle mouth. There are corks, plastic plugs, glass plugs, etc. Since corks are elastic, compressible, airtight, watertight, and have low thermal conductivity, they can provide good plug seals and are ideal natural materials. As substitutes for corks, there are concave plastic plugs with or without ribs, and plastic plugs with ring skirts that adapt to the gradual change of the bottle mouth diameter, which can ensure more effective plug seals.

?4. Buckle seal

Elastic LDPE and PC bottle caps can be snap-fitted to the bottle mouth. The so-called snap-fitting means that the bottle cap pressed against the bottle mouth tightly bites the bottle mouth sealing ring, so that the entire surface of the ring edge becomes the sealing surface. The greater the elasticity of the plastic, the tighter the fit with the sealing ring, and the better the sealing effect.