When manufacturing plastic caps and closures, Top gate, side gate, and inside gate all reference the location where the molten plastic material flows into the injection mold cavity, commonly known as the cavity entrance. It is the small-restricted opening connecting the runner (that’s the name for the pathway of the plastic material through the injection molding machine) to the cavity in the plastic closure molding tool. It is important to note that every injection mold design must have at least one gate and the position of the gate directly influences the appearance of the finished product.
There are three common gate locations used with injection blow molding of closures – which are the side gate, top gate, and inside gate. The gate mark is intended to be small and barely visible, but it does often leave a small dimple on the closure. Typically, this only creates a challenge for market applications that require a very high gloss finish for shelf appeal – or for applications in which a label will be affixed to the top of the closure.
The Different types of gates:
The Side Gate
The side gate is one of the more common gate designs. No confusion intended here – the side gate is located on the side of the closure. The material is injected through a gate on the side of the closure; it is commonly used for multi-part dispensing closures such as disc top closures, flip top closures, sprayers, and pumps.
The top gate is formed through material that is injected through a pinpoint gate on the forward part of the closure. The top gate leaves a small nub in the middle of the top of the closure (or commonly referenced as the exterior top surface); the top gate is used with a wide range of continuous thread and deep skirt closures (screw on caps), and large size flip top closures.
The material is injected through a gate on the inside of the closure, which leaves a mark on the inside of the closure rather than the outside of the closure. If shelf appeal is what you are after, a closure with an inside gate allows the container to have a smooth top (common requirements for cosmetic, personal care, and high end products). The inside gate is a good option if you are looking for flawless label adhesion and is primarily used for cosmetics and high end products that might not present as well with a visible gate mark on the top surface.