Plastic Coating

Keeping containers closed with an airtight seal was much harder before the invention and widespread use of plastic. Did you know that most containers had to use metal lids? And if an airtight seal was necessary, the lids had to be shrunk and sealed much like the process of canning food into traditional glass jars. Plastic has taken over most of the packaging world. There are good reasons behind this. Plastics are inexpensive, durable, and easy to make completely airtight. Factories all over take advantage of the benefits that these plastic containers can bring.

Many closures for containers are made from plastic. These have become a popular choice for the temporary closing of containers in use and for previously-opened containers. The plugs prevent the contents of a container from leaking out and help extend the life of the product inside the container. These plugs can create an airtight seal that is ideal for preventing the evaporation of liquids and contamination of the product that is stored inside.

A variety of factories help create their own customized plastic plugs for specific applications. But there are four main types of plugs that most factories can use for different scenarios. Most of these prevent the need for creating customized stoppers for different containers and products.

Tapered: These plugs are designed to fit in a simple opening. They are narrow at one end and they expand to a larger size on the other end. This makes them easy to place into a hole and plug it up without having to worry about the plug falling into the containers.

Push-fit: These plugs are similar and are designed to fit flush with the exterior of the container.

Cylinder valves: These valves are designed to be used as closures and are usually used with volatile materials, like gasoline.

Threaded plugs: These are used to screw in container openings. This provides an airtight seal that will not pop out of place.

Plastisol uses a unique formulation process that suspends PVC particles in a plasticizer. The plastic is heated to 177 degrees Celsius, which dissolves both the PVC and the plasticizer. Next, the mixture is cooled to 60 degrees Celsius. This creates a plasticized product that remains permanently flexible due to the dissolved properties of the plastic. Often, this plastic is used for molding, but it has a variety of other uses as well.

Plastisol is often used in the manufacturing of roof coatings, furniture coatings, screen printing, and textile ink. Plastisol is often used for dip molding, because it coats objects in a flexible coating that is both attractive and durable. Industries use plastisol coatings for a variety of tasks, such as coating tools, protecting surfaces, creating waterproof barriers, and protecting delicate parts from impact.

Surprisingly enough, many of the printed images on modern clothing is created from plastisol coatings melted into the fibers of the fabric. Plastisol is perfect for screen printing because the plastic soaks deep into the fibers of the fabric, allowing the image to stay in place longer. Plastisol will not dry on its own, but requires a curing process to harden the plastic. Plastisol-coated clothing must be cured in an oven before it can be sold in retail locations.

Another popular use for plastisol is as a material for slush molding. In slush molding, the plastisol is placed inside a metal mold, which is then spun rapidly to force the plastic to take on the shape of the mold. The mold is then heated and excess plastic is poured out. This creates flexible, hollow molds perfect for a variety of industrial and commercial uses.

Most plastic caps and many other plastic closure types are created using large industrial injection molded plastic machines. Injection molded plastic injects a small amount of plastic into a cap-shaped mold. The plastic is then dried and released from the machine in one smooth motion. Watching a plastic cap machine in first-person action is an interesting process. It is amazing to see how humans have been able to transform basic parts into fully-functional parts that can create other useful tools and pieces for everyday life. Many plastic cap machines can create hundreds or even thousands of plastic caps within just a minute or two.

A plastic closure machine works something like this:

The plastic pellets are added to a large hopper in the machine. The hopper melts the plastic and carries it to the part of the machine that will inject the hot plastic into the mold.

32 or more rotating piston molds rotate around a central motor. The plastic is injected into the molds in one smooth motion by the pistons as they travel around in a circle. The pressure from the two sides of the piston give the plastic caps the desired shape and quickly dry the plastic until it is hard enough to release from the mold.

In one smooth motion, the pistons release the cap at just the right moment and it releases into a metal passageway that directs the cap into a storage bag or another conveyor belt. The process is so fast, that there are always at least 4 or 5 plastic caps inside the chute at any one time. Most machines can create thousands of plastic caps in just a few minutes.

Depending on the machine, it is possible to program the machine to create caps of varying sizes and specifications. Some machines can create threaded caps, while others create pop-off caps or plugs only.