Liner Materials

Closure Viability Depends on Selecting the Proper Liner.

Because the liner facing is in direct contact with the product, chemical compatibility is crucial. It is important to provide a good liner system to maintain the integrity of the product for its required shelf life. The incredible variety of packaged products has led to the development of many liner systems, and modern research is constantly developing new concepts.

Liners are either die cut and inserted, molded or flowed in for lug, continuos thread, pressed to seal/twist to open and various specialty closures.

Whether termed a liner, innerseal or gasket, all liners are made of a material designed to seal a container and protect the product after the closure is applied to insure that the packaged product reaches the customer in an acceptable condition. In addition, some liner types, such as innerseals, are designed to add evidence of product tampering. Liners vary in type and material according to specific customer and product requirements.

Liners for metal closures consist of several types. These basic classifications are: Paper composites Plastisols, synthetic foams and solids and rubber ring gaskets Innerseals; e.g., glassine heat induction liners, pressure sensitive

Liner materials for plastic closures can be grouped into three categories:

• Cellulosics
• Foils
• Extruded polymers

These categories are not always sharply defined, and many combinations of various materials are used to accommodate specific requirements.

A seal can also be achieved in many instances by using a closure that incorporates a specific molded-in feature such as rings, plugs or flexible sections. These features achieve a seal by conforming to one or more of the sealing surfaces on the container neck finish.

The five general areas of sealability on the container neck finish are:

• The top sealing surface
• The interior vertical surface
• The inside edge
• The exterior edge
• The exterior vertical surface

The seal is of the utmost importance when considering the total package. If the seal is not achieved and maintained by the sealing system, the retention and integrity of the product may be jeopardized.

Proper closure/container system selection needs to address many issues and concerns, and should be discussed. To illustrate the magnitude of problems surrounding liner selection, here are some factors that may need to be confronted:

If the product contains acid, or caustic materials it will attack some liner materials, but others will withstand this readily. Solvents will easily permeate some materials, but not metal foils, or some plastics. Essential oils used for fragrance can also react in a similar manner. Some products are a mixture that requires protection in several directions. This situation may call for a composite of liner facings that when laminated together provide the right combination of protective factors. Autoclaving, or exposure to high heat, will require a liner facing to withstand these temperatures, and moisture conditions. If the product is a food, or drug, or an injectable, the liner must meet government regulations for sanitation, and safety regarding ingestion, or injection into the body. Creating a barrier against oxygen, or other gas permeation, may be critical. The liner facing is an important area of defense to assure this barrier.

Pulp/Aluminum Foil

This material is relatively free of odor and taste problems. Used for non-acid, non-alkaline products. Has been used for organic solvents, chrome cleaners, brake fluids, mineral oils, among other products.

Pulp/Tin Foil

Possesses good resistance to hydrocarbons, alcohols, ketones and oils. Not good for acids and alkalis.

Pulp/Polyvinyl Lubricant Film

Good general purpose liner for food, beverage, medical and chemicals packed at less than 120 degrees.

Pulp/Saran Lubricant Film

High chemical resistance. Excellent gas and moisture vapor transmission resistance. Good taste and odor resistance makes it a good choice for cooking oils and salad dressing.

Solid Polyethylene

Good chemical resistance and low moisture vapor transmission rate. Used widely for non-oil products filled at room temperature.

F-217

A laminate liner composed of a foamed low density polyethylene inner core and high density outer surfaces. Excellent chemical resistance and low moisture vapor transmission rate. Good taste and odor resistance.

Pulp/Oil Paper

Heat resistant to 80 degrees. Good resistance to moisture permeation. Used for pickles, olives, cherries, vinegar, etc.

Plastisol

Provides excellent resistance to mild acids as in food products. Permits "hot fill" operations to effectively produce a vacuum seal. A properly selected Plastisol is particularly useful for processed foods because it resists food acid and will withstand sterilization.

Induction Sealing

Induction sealing is a noncontact heating process that accomplishes the hermetic sealing of a container with a closure that includes a heat-sealable foil laminate. The typical induction innerseal begins as a multi-laminate liner inside a closure. It consists of a layer of pulpboard, a layer of wax, aluminum foil and a layer of polymer that is compatible with the bottle material and capable of heat sealing to the lip of the container. When the closure is placed onto the container and is passed through an electromagnetic field produced by the induction heater, several things occur. An electromagnetic current, called an eddy current, is induced into the foil portion, resulting in a resistance-type heating effect. The heated foil melts the wax layer, which is absorbed into the pulpboard, releasing the foil from the pulpboard, and the polymer coating melts, hermetically sealing the foil to the lip of the container.

LINERLESS

Though most Polypropylene Closures are lined, in controlled circumstances linerless closures eliminate the cost of material and inserting of liners. The economies can be worthwhile. It is important that the neck finish of the container mates properly and consistently with the closure. Pre-testing and "on-going" quality control checks of both the container and closure are important when you choose this option.