Understanding forming, filling, sealing and lidding operations

Whatever the size and shape of the pack, a means of either pre-measuring or weighing the product or product dose going into, say, a vertically filled pack is required, or the already bottom sealed pack is lowered onto a precision weighing table and the product to be packed is dispensed until the gross weight of the product filled pack has been reached, at which time the filling stops and the top is sealed (which also forms the bottom seal of the next pack) and the pack is cut from the web. It will then go on for boxing and shipping.

There are different sealing methods available (heat, adhesive, crimping) depending on the packaging material being used and the application. Such a range of requirements, in turn, means there are many different types of machines used to form, fill and seal the variety of packs, to wrap products, or to apply lidding (Figure 6.1). 

The nature of the product to go into the various types of flexible packaging will also have an impact on how the printed reel or lid is formed, filled and the pack sealed. Is it a liquid, a powder, granules, cream, paste, a solid, soft or hard? How does that impact on the machine design and operation? What kind of transporting system, hopper, weighing or dispensing arrangement is required to bring the product to the filling machine and each individual pack?

To reduce crushing of the product in transit and use, extend shelf life, or perhaps retard the growth of bacteria, the final sealing process may require the bag, sachet or pouch to also be filled or inflated with air from a blower or from an inert gas supply such as nitrogen . which is a natural means of extending shelf life.

In addition, there may be a requirement to provide tear notches; to cut out hanging holes or slots; to provide carry handles, to add a recloseable feature; to provide some kind of spout or pouring device. For some applications the filled packs are not separated, but rather perforated and supplied in strips for individual packs (sachets) to then be removed and used progressively, such as from a hanging display.

The packaging machines that form, fill, close and seal a flexible package in one continuous or intermittent-motion operation can be configured so that the printed web travels horizontally through the machine (horizontal form-fill-seal) or vertically through the machine (vertical form-fill seal).

Fed from a roll, the web is folded to the desired package shape and stabilized by heat sealing. The product being packed is placed into the formed package, and the remaining opening is sealed. There are many different types of machines that perform these operations.

Rather than trying to describe and discuss all the many different types of forming, filling, sealing, wrapping or lidding machines, this Chapter simply aims to explain the principle of the main types of equipment on the market. These can perhaps best be summarized as:

VERTICAL FORMING, FILLING AND SEALING

Vertical forming, filling, and sealing machines are fairly complex, yet flexible and versatile machines used in the packaging industry to package various types of free flowing food, oils, powders, other materials and a wide range of liquid products.

Speed of packaging, ease and convenience of changeovers, machine reliability, low maintenance, and low operational costs have all helped to advance their popularity of this type of equipment. Other important factors include software oriented operation, increasing demand from the food and beverage sectors, chemicals and personal care industries, and growing demand for convenient packaged consumer products.

These types of machines enable the packer to have a vertically operated packaging system in which:

• The printed flexible packaging material is formed into the required sachet, bag, tube or pouch shape, the two outer edges of the pack being joined together with a longitudinal or vertical seam
• The bottom edge of the pack is also then sealed
• The weight or volume of product being packed is measured
• The already formed shape is filled with the product
• The top of the newly filled package is sealed. 

This can perhaps best be illustrated in Figure 6.2.

Vertical forming and filling means there is no need to have a large amount of floor space available to place the machine when compared with horizontal machinery. They are therefore quite compact.

Packs made on this type of equipment are either normally flat, or made to incorporate gussets at the sides, or provide block (flat) bottoms to enable the pack to ‘stand up’ on the retail shelf or in the consumer’s cupboard or fridge. Both types have a large flat front and back surface that will enable printing on both sides of the pack (albeit that the back of the pack will usually have a vertical center seam area that is not printed on), making the most of the available space. Two key types of vertical form, fill and seal machines are commonly used:

• Single web machines
• Dual web machines.

Single Web Machines. The manufacture of a vertically formed-filled and sealed pack is illustrated in Figure 6.3 and starts with the flat printed web approaching the back of a long hollow conical tube. This is known as the forming tube. As the center of the web approaches the tube, the outer edges of the substrate form flaps that wrap around the forming tube. At the same time, the web is pulled downwards (this is where the correct coefficient of friction/slip is important (see Chapter 4) around the outside of the tube and a longitudinal/vertical sealing jaw clamps onto the edges of the web to create a ‘Fin Seal’, bonding the edges together by melting the seam edges together or by using an adhesive. Ultrasonic sealing is a new development which tends to be used for heat-sensitive products and permits sealing through liquids.

At the beginning of the bag filling process, a horizontal cross sealing jaw creates the ‘bottom seal’ by clamping and sealing across the bottom edge of the now tubular bag. This bonds the bottom edges together, and cuts off the previous filled bag and/or any bag material below the seal.

The feeding of the web of material and cutting of the bag/pouch depth to the correct size can be determined either by pouch length, or by indexing to a photo registration mark, which is then detected by a visual sensor.

The product being bagged is now dispensed through the long conical filling tube into the center of the bag. When the right content quantity of the product-filled bag has been reached the filling stops, and the horizontal cross sealing jaw seals the top of the bag. Any required product finishes, such as hole punching for retail hanging racks, will be done concurrently or just after this ‘top seal’ is made.

At the same time this also simultaneously forms the bottom of the next bag being formed above. The filled and sealed bag can then be cut off from the tube to provide an individually sealed package, which is then free to move onwards into the required filled product packing and shipping operations.

It should be noted that each bag, pouch or sachet material, as well as the specific end-use application, has a bearing on the heat, pressure and dwell time sealing jaw settings necessary for creating the filled pack. The preciseness in which these three factors are controlled and balanced will determine to a great extent the quality of the seal.

The amount of time the seal jaws are closed and in contact with the sealing material is generally defined as the ‘dwell time’. This is adjustable on most forming, filling and sealing machines and is a tool to ensure the correct temperature is obtained on the sealant film.

The pressure applied between the sealing jaws when the heated surfaces are in contact with the material is also a critical adjustment, ensuring that the material is held in place without wrinkling until the heat is driven into the seal area. Excessive heat/temperature can create as much problem in producing a continuous heat seal as too little heat If sealing issues arise it is important that the heat, pressure and dwell time characteristics are adjusted during trouble shooting to uncover the root causes. A change to any one of these factors will mean that one or both of the other two must also be adjusted to compensate for the change.

A single lane machine format is used for various sizes of pouches or bags as it forms a single pouch during each cycle. Multi-lane format machines create multiple pouches in each cycle. They are used for multiple small packets such as small salt and sugar packets.

Recent advances in bag, pouch and sachet forming machines and systems technology have enabled even smaller and smaller vertical form, fill and seal machines to be developed. In particular, multi-lane sachet machines are now being used in a multitude of industries for small quantities of powder and liquid products. Sealed on all four sides, these small packets are often filled with condiments and spices like salt, sugar, mayonnaise, or ketchup.

Manufacturers and contract packagers love sachet machines because they can achieve high throughput while occupying limited floor space. The operation of multi-lane sachet machines is similar to that of other form, fill and seal machines, but with a few notable differences. Basically, a large roll of film is unwound by motor driven rollers and kept in constant tension. It is then slit into two halves which are brought together and formed into multiple sachet packets, filled with the product, and then sealed, all in a vertical fashion, at rates of up to 80 cycles per minute, per lane.

A group of pneumatically-driven disc knives can then cut the film vertically if individual sachets are desired. A horizontal cutting station then separates the filled, sealed, and longitudinally cut packets into individual sachets. A single sachet machine with the capacity for up to 10 lanes can produce up to 800 packets per minute, or about 13 per second. However, the more lanes there are on a multi-lane sachet machine, the fewer opportunities there are for narrower web converters.

Dual web machines. Dual web form, fill and seal machines are used for the manufacture of four side sealed bags or pouches, as well as for packs that require a different materials to be used on each side. Dual web systems use two rolls of material instead of one, which are fed in from opposite sides of the machine. The bottom and sides are heat sealed together to form the pack, and the product is again loaded from the top. The pack with the loaded product then advances downwards; the top is sealed and the pack is cut off. As with single web machines, the sealing of the top of the pouch forms the bottom of the next pouch. During this process a tear notch or a hanging slot may be added.

Whether single web or dual web, vertical forming, filling and sealing machine may be divided into single, multiple lanes and open and closed machines.
In terms of the end-use industries and applications vertical forming, filling and sealing machine are used in, these include:

• Food and beverage industries for tea, sugar, wafers, and candies
• For fresh vegetable packaging and pouches for sauces and detergents
• For chemical and pharmaceutical industries for various packaging purposes
• The packaging of bulk goods such as nuts and cookies
• For powdered goods such as coffee, for grains and granules such as detergents
• For tea and liquids such as ketchup, and gel.

HORIZONTAL FORMING, FILLING AND SEALING

In addition to vertical form, fill and seal machines, there are also horizontal packaging machines that work in roughly the same way. Closely related in terms of overall operation, horizontal form-fill-seal machines will generally use more floor space than a vertical system, with all the stages of unwinding, slitting, folding, sealing, cutting and filling carried out in one horizontal inline operation. This can be seen in Figure 6.4.

As can be seen, the horizontal form, fill seal machine has a reel unwinder on which the web is mounted. As the web is released from the unwinder it passes through a forming plough and is then sealed at the bottom and the two sides. A cutter will cut the pouch vertically at the right time, being controlled by a photocell. An opening device then opens the pack and brings it to the filling station. The top stretching mechanism stretches the pouch or pack to make a clean top seal before the packs or pouches are discharged. It is an intermittent system in which the pack is sealed on three sides and then later filled and sealed on the fourth side.

Some horizontal form, fill and seal packaging solutions include thermoformers that produce a variety of packaging types. These types of horizontal form fill seal machines produce flexible to semi-rigid and rigid packages capable of vacuum, modified atmosphere packaging (MAP) and much more.

Many food filled packages are filled with nitrogen to extend shelf life. Food manufacturers are often looking for ways to improve their geographical reach or otherwise extending the shelf life of their product without the use of chemicals. Nitrogen filling is a natural means of extending shelf life. More and more manufacturers are choosing to create and control their own nitrogen supply by using on demand nitrogen generators.

Stand up pouches are also made on horizontal form, fill and seal machines using a film or a laminate, giving the packaging an aesthetic appeal. Other features can be added to stand up pouches, such as a spout, zip or a straw. Spouted pouches are either top spout or edge spout depending on the requirement.

Spouted pouches are used for products which are commonly free flowing liquids and pastes. Zipper pouches are used when the pouch needs to be reclosed after a required amount of product has been used so that the product remains fresh for a longer duration or retains certain properties like aroma in coffee. Straw pack is also another application wherein the straw is already made available within the pouch. The most common application for this is in beverage pouches.

FLOW WRAPPING MACHINES

Pre-printed wrappers and decorative bands applied on flow wrapping machines are an effective way of packaging and branding products. Such wrappings are typically used on confectionery, sweets, gift wrapping, butter packs, etc. In many cases products are completely over wrapped in paper, foil or film to form an airtight seal.

Flow wrapping machines provide a close fitting and air tight bag or pack around the product being packaged. They are horizontally operated, with the packaging material mounted above the operating level. Typically, the product is loaded horizontally with a longitudinal seal formed below the pack. This can be seen in Figure 6.5

Every flow wrapping machine has an infeed conveyor, a film feed assembly (backstand), a film forming area (former), a centre and bottom seal (finseal), a cutting head and a discharge area. Food and non-food products packed by this type of flow wrapping equipment are placed on the infeed conveyor. This can be done by hand feeding or by using a semi- or fully-automated feeding solution.

An infeed conveyor delivers product to the forming area, where film is drawn from the film feed assembly into the forming area. A tube is then formed around the product and a finseal created. The film tube, now containing the product, is then delivered to the cutting head. The cutting head creates the end seals while it cuts apart adjoining wrapped products into individual packages. These are delivered to the discharge area, from where they can be either cartoned at a packing station or accumulated for packing at a later time.

Both flow wrap and over wrap methods typically use polypropylene film (BOPP) to create the wrap, although other film, foil and paper substrates can also be used.

Cold sealing methods are used, particularly in confectionery applications. The adhesive is coated onto the material. During the wrapping process the material is folded onto itself and sealed via a sealing wheel.

LIDDING
The range and variety of flexible lidding applications and machinery is quite large and continues to expand. Flexible lidding today, is used for packaging an enormous variety of foods, as well as medical items, pharmaceuticals, health, beauty and personal care products, hardware, small electronic parts and much more, in containers such as tubs, pots, trays or jars. Typical lidding materials include paper, metalized PET or PP. Quite widespread is the use of aluminum foil for lidding, particularly for water cups, dry foods, yogurt pots, ice-cream, etc. A typical lidding film construction is illustrated in Figure 6.6.

Choosing a lidding film can be a complex process as many things need to be considered: the type of seal, the seal strength, oxygen- and moisture-barrier requirements, and anti-fog requirements for the application. There’s also film thickness, the ability to seal through overfill, the type of container, the backing substrate, the ingredients inside the packaging, shelf life, sealing equipment, compliance requirements and the application conditions. All of these elements must be understood fully in order to ensure that the proper lidding material and sealing method are selected for a successful application. Quite simply, the packaging converter needs to sit with client to review all the lidding requirements, the substrates to be used, laminate constructions, sealing methods and legal requirements, and from this undertake any necessary due diligence on materials and production.

Lidding films not only seal and protect the product but can perform an important decorative, marketing, legislative and informational function. Most lidding materials are designed to be peelable to allow easy access to pack contents (Figure 6.7). Peelable seal lids require a polymer layer on the inside to facilitate the heat sealing.

Some lidding applications require a heat seal coating applied to the film construction. The coated film passes over a pre-heat station where it is warmed before it is sealed to the tray or pack, via a sealing bar or platen set at a desired heat, pressure and dwell time. The sealed tray or pack is then die-cut to shape. Lids with peelable seals can be produced to adhere to almost any material that a pot, tub or tray might be formed from. Pot applications such as yogurts use heat seal pre-cut lids or diaphrams matched to the shape of the container.

Adherence of lidding materials to a specific pot, tub or tray and the resultant seal integrity requires a solid understanding and expertise in both film, tray and fill/seal assembly. Commonly, the lidding film will be reverse surface printed before lamination. Consideration must also be given to how the product is loaded and fed into the pots, tubs or trays in the machine, as well as how you the filled packs are handle the once sealed.

In a book of this type it is not proposed to go into all the different types of filling and lidding machinery. Some machines use in-line thermoforming to form a tub or tray, fill this with the product being packed and then apply and seal the lidding materials (see Figure 6.8).

Rather than forming the tubs or trays in-line on, the lidding machine, other types of lidding machines may start with nested ready pre-formed or molded pots or tubs. The machine will then start with a denesting process, placing the individual tubs on an in-feed for filling, then applying lidding from a continuous web or stack of die-cut lids, and once again sealing and cutting.

If required, the complete line may also apply date, time, use-by or other overprint requirements. If Modified Atmosphere Packaging (MAP) is also required, then the machine will need to be fitted with a vacuum and gas flushing system. These systems allow the air to be replaced with a gas mixture during the seal process. Normally MAP capability is defined at the outset when purchasing a machine, but most machinery suppliers can retrofit this capability if needed.

Sealing of lids is undertaken using heat sealing. Heat seal and lidding adhesives for packaging can be supplied from a number of chemical companies with very different attributes. To select the best adhesive for a specific application, it is important to consider both the end use and the converting machine process that makes the final seal.

The specific type of adhesive selected for a project is important because the substrate to which the adhesive is applied is most often different than the substrate with which it needs to bond.

Understanding the filling and sealing equipment is also critical. In addition to the proper activation temperature for a given adhesive, consideration needs to be given to the amount of pressure being applied at the temperature required to complete the seal, and the dwell time (the duration of time that the heat will be applied to the adhesive) . both of which are factors determined by the equipment and processes. Both will have an impact on the types of adhesives recommend.