Comparative Experiment of Airtightness: Clip type VS Lever Ring type Closure, Silicon VS PTFE Gaskets

Nitto-stainless has several types of lids for stainless steel containers:
One kind of open type and two airtight types.


2 types of airtight containers

Clip Lid (Model CTH)

Easy-to-handle clip type. It can be fastened with one hand.
The standard model of gasket is attached to the body side of the container.
The lid is fixed with 3 ~ 6 clips according to the size of the container.


Lock Lever Ring (CTL Type)

Lock lever ring is easy to be put on and take off. It needs to be handled with both hands, but it can be put on and taken off quickly.
Put the gasket on the lid side.
Regardless of the size of the container, the lid can only be fixed with one ring.


FAQ: "Which lid seals better?"

In the inquiries we receive from our customers, we receive a question regarding sealed containers, “Which lid is more tightly sealed, CTH or CTL?”.
As a premise, our airtight containers are designed on the basis of “an airtight seal that prevents spills of liquids or powders that are stored inside”.
It is not designed to achieve an absolutely-complete airtight container that even gas does not leak.


For example, when storing a gas-producing liquid, the liquid inside does not leak when the container is tilted, but it is quite possible that the gas generated inside the container leaks during storage.
If you want to seal the gas tightly, we will introduce you a pressure vessel.


We actually conducted an experiment to compare the tightness of the containers.

The outline of the experiment is as follows.

  • Place containers in rooms with controlled humidity and temperature.
  • Put anhydrous calcium chloride, which is also used as a desiccant, in a container.
  • Measure the weight of a container after it has been left for a certain days.

Even if it is an airtight container, when it is installed in a room with controlled humidity, moisture in the air gets into the container through a small gap between the lid and the gasket.
In addition, anhydrous calcium chloride absorbs moisture entering the container, and the weight increases by the amount absorbed.
The lower the airtightness of the container, the more moisture gets in and the weight of the container changes greatly.

By measuring the weight of the container through this method, the degree of sealing can be compared.


Experiment content

Containers used in the experiment

  • Clip Type Sealed Container (20 L Type)
  • Lever Band Type Sealed Container (20 L Type)

Both containers were equipped with 1000 g of anhydrous calcium chloride, and the weight was measured at regular intervals in a constant temperature and humidity room controlled at 20 ° C and 50% humidity. (60 days)

Experimental result

The orange line is the clip type CTH -30 and the gray line is the lever band type CTL -30.
The graph shows that the weight of the lever-band container changes less.
In other words, when comparing the clip type with the lever band type, this experiment revealed that the lever band type has a higher performance of sealing.
Comparing the two sealed containers, the performance of sealing is about twice as different.



The gasket material used to maintain airtightness is silicon, so the conditions are the same.
The difference in sealing performance between pressing the gasket with four clips and pressing the entire circumference of the lid with a lever ring probably caused this result.


Additional experiment of PTFE gasket

Nitto-stainless  also have storage container [Model CTH-PTFE] with PTFE gasket using high chemical resistance PTFE material.


Features of Storage Containers with PTFE Gasket

PTFE material is not affected by most chemicals.
Even be soaked in hydrofluoric acid, which is known as a dangerous poison, PTFE material cannot be dissolved, so drugs can be stored safely.
This container is ideal for handling strong chemicals, but we have to remind our customers that, since PTFE is a kind of resin gasket, its airtight performance is weaker than a rubber gasket.”.


Experiments to determine its poor sealing performace

We also examined the sealing degree of the storage container with PTFE under the same conditions as the sealed container with silicone gasket.

It’s clear that the sealability is inferior compared to clip type and lever band type.
It has more than 4 times less airtightness than clip type and 9 times less airtightness than lever band type.

In terms of water vapor permeability, PTFE is said to be 680 times less permeable to moisture than silicon. (PTFE is also used for the material called Gore-Tex which is used for raincoats.)
Comparing by these figures only, it seems that the PTFE material has a higher degree of sealing, but the actual sealing tendency was reversed.
The difference in the results is probably due to the gasket’s stiffness.



The silicone gasket is elastic like rubber, while the PTFE gasket is hard and non-elastic.
Hard gasket has less elasticity comparing to the soft one when adhere to the lid.
Since the material itself has low water vapor permeability, it is difficult to imagine that moisture permeated the packing itself, and it is considered that moisture permeated through the grounding surface of the hard lid and the hard gasket.



As a result, we found that there is such a difference in the degree of sealing.

Lock Lever Ring Type > Clip Type > > Storage Container with PTFE gasket

Since this experiment is conducted using moisture, it is thought that separate experiments are necessary for oxygen and other gases.
In addition, as a premise, the sealed container is designed not to spill liquid or powder.

Comparing the 2 types of sealed containers, there was a 2-fold difference in performance, but it can be said that the experimental results show that the weight of the container changed only about 1 g in 30 days.
The container is suitable for storage and storage as long as it is not used in an airtight manner.

*This article can only be used as reference.