I recently received a prototype for a two-piece lid/rim mechanism I’m developing for a cosmetic container, and overall the concept seems like it can work.
The purpose of the cover is to gently stir/agitate only the top layer of a very thick body cream as the customer twists the cover during the initial opening of the package. This is primarily to create the desired appearance/texture of the top surface when the customer first opens the product.
The prototype is currently made from a relatively hard plastic, so it is somewhat difficult to insert into the rim of the silicone liner. The intention has always been to eventually manufacture it in a softer/more flexible plastic or similar material, which I expect will make installation easier.
However, I’ve run into a different issue that I think may have more to do with the very thick viscosity of the body cream than with the prototype itself.
When the components are outside of the cream, the lid rotates very easily against the rim.
Once everything is assembled with the thick body cream inside, however, twisting the lid sometimes causes the entire silicone liner to rotate against the ceramic container, rather than the lid rotating relative to the rim as intended.
I attached a ChatGPT drawing to illustrate this. The red squiggly lines represent the areas where rotation is currently occurring versus where I want the rotation to occur.
My current theory is that the friction/resistance between the silicone liner and the ceramic container is lower than the rotational resistance created by the thick cream against the lid. Therefore, when I twist the lid, the system takes the easier path and the silicone liner rotates inside the ceramic.
Does that logic sound correct?
I’ve been thinking about a few possible solutions:
1. Increase friction between the silicone liner and ceramic container. Possibly by adding some type of removable adhesive, tacky surface, friction feature, or other method of preventing the liner from rotating.
2. Redesign/enlarge the plastic rim so that it grips or indexes directly against the stationary ceramic container rather than relying entirely on the silicone liner. This is probably my preferred solution if feasible. The challenge is that the lid still needs to rotate and interact with/stir the cream.
3. Change the material of the lid/rim assembly.
The prototype is currently hard plastic, but the production version was already intended to be somewhat softer/flexible. I’m wondering whether a softer material could reduce the resistance created as the lid moves through the thick cream.
- Attach the silicone component to the plastic rim/lid assembly.
My chemist suggested bonding/adhering the silicone piece to the plastic component. I’m less convinced this solves the underlying issue, because the resistance from the thick cream would still be transferred into the assembly and could potentially continue rotating the liner.
Ideally, I would love for the rim/mechanism to mechanically grip or register against the ceramic container, so the ceramic becomes the stationary reference while the lid rotates independently.
I’m not sure whether that is realistic given the geometry, though.
For anyone with experience in mechanical design, packaging, injection molding, silicone/plastic interfaces, rotational mechanisms, or friction-fit assemblies, which direction would you explore first?
Is increasing the friction between the silicone liner and ceramic likely the simplest solution, or would you redesign the rim so that it mechanically engages the ceramic itself?
https://www.image2url.com/r2/default/videos/1788436554230-13b3c342-2fdc-4aa3-a427-e1b7301a632c.mp4 this video link also shows the problem