Distribution and storage
Distribution and storage comprise those activities occurring between the point at which the product is packed and its ultimate point of sale in the retail store, supermarket, vending machine, pharmacy, etc.
At the end of the packing line the packages are collated by hand or by machine in groups of 6, 12, 24, etc. for packing in a transit package. This may comprise:
• A shallow-depth paperboard tray which is subsequently stretch or shrink wrapped in film.
• An open-ended corrugated fibreboard sleeve which is subsequently stretch or shrink wrapped in film.
• A corrugated case with glued or taped closure. There is also a shelf-ready corrugated case which has a crocodile-type opening and is designed to go directly on the supermarket shelf.
• A unit of 6/12/etc. packs simply shrink wrapped in film with no additional paperboard protection.
These transit packages are usually palletised, alternate layers being packed in a different pattern or plan to give stability to the load. The pallet load may be further stabilised with strapping or stretch film.
Standard retail pallets are reusable with a common size being 1000×1200 mm.
Pallet loads are stored in warehouses which may or may not be heated. Frozen and chilled foods are stored in appropriate conditions, i.e. –20 °C to –35 °C for frozen products and 0 to +3 °C for chilled products. Storage is usually freestanding, limited to two pallets high, or in racking.
It is unusual for full pallet loads to be delivered directly from the manufacturer to the retail store except in the case of very large stores. Pallet loads are usually distributed to:
• Distribution warehouses of major retail organisations. These are strategically placed to meet the stocking requirements of a number of the company’s stores in a given area. Mixed loads are “picked” or made up to meet the needs of the respective stores. This means that mixed numbers of transit packages of different products are placed in special cages, often in a somewhat random arrangement.
• Distribution warehouses of companies which are independent of both the manufacturer and the retail stores. The procedure for distribution is the same as that described previously.
• Distribution warehouses of independent cash and carry companies. These companies display pallet loads of goods in bays or racking allowing small retailers to pick the goods for themselves. This type of distribution has led to a more attractive cash and carry transit package, e.g. shrink wrapped to allow the more attractively printed individual cartons to be seen, or by the use of pre-printed white liners for corrugated cases.
Key paperboard characteristics
The main requirement of both the individual carton or other forms of packaging is for stacking, handling, and transit protection. Stacking requires vertical compression strength. That may be assessed under static or dynamic loading on a pallet, a transit package or an individual package. Handling of transit packages requires strength to resist impact and uneven compression in mixed loads.
Transport hazards usually refer to impact and can be checked on sliding planes or by drop testing. Some sensitive products may need special cushioning protection and the needs can be assessed on variable frequency vibration tables and by the use of special records in practical transit tests. Vibration can cause damage to the package by scuffing or rubbing adjacent surfaces.
These requirements may also have to be met in frozen (–20 °C to –35 °C), chilled (0 to +3 °C), very damp or wet conditions, or very hot and dry conditions.
In general the strength-related properties are:
• moisture content
• compression strength (short span)
• box compression strength
• water resistance (frozen and chilled food distribution).
Distribution and storage in practice
The following factors are essential to good distribution and storage:
• The strength of paperboard
• The structural design of the unit package
• The nature of the product, i.e. if it contributes to the strength of the package
• The strength and structural design of the transit package
• The pallet plan. The dimensions of the unit transit package can now be examined by computer to give the optimum utilisation of the pallet volume. This also leads to the best stacking performance as a result of close and interlocked packing on the pallet.
Some additional comments are, however, necessary for particular conditions of storage and distribution, see the following page.
Appearance needs are provided by surface and structural design. Performance needs relate to printing, conversion and use. This may involve special protection or functional requirements relating to the paperboard product or to any other products with which it may be in contact, or to the handling, storage and use of the product.
Design in the broadest sense highlights every need which must be incorporated into the choice of paperboard for every graphical or packaging product.
|Frozen food and ice cream
||The storage temperature will be around –20 °C. The printed or varnished print must not craze at this temperature.
||The storage temperature is 0 to +3 °C and the main hazard is the very high relative humidity which raises the moisture content of the paperboard with a consequent loss of stiffness and strength. There are a number of ways of reducing this effect such as by using a tight sleeve where the product is in a plastic or aluminium foil tray, or by packing the product directly into a plastic coated paperboard tray with a printed heat sealed plastic coated paperboard lid. The paperboard can be made more resistant to moisture by:
• Hard sizing all layers of the paperboard, thereby improving its edgewise wicking tendency.
• Functional coating with plastic, aluminium foil, wax or moisture resistance varnish.
|Very damp or wet conditions
||The paperboard can be given enhanced moisture resistance as discussed under “Chilled food”. These conditions also demand a coating on the paperboard and a choice of compatible inks and varnish with good keying, wet rub, and scuff resistant properties.
|Very hot conditions
||Here the main problem to arise is blocking, i.e. the sticking together of sheets or packages. It is avoided by the choice of a suitable paperboard coating and compatible non-blocking inks and varnish.
Edge water absorption, Wick test
Click to enlarge.
In many wet applications such as deep-freeze packaging, or for drinking cups, a higher degree of water resistance is needed. Examples of the most demanding applications might be the packaging of hot spinach, or cups for tea or coffee. Even if the inside of the package or the cup is plastic coated, the edges normally remain exposed. The Wick test is the method commonly used to evaluate water absorption via the paperboard edges.
The mechanism involves capillary attraction, which is reduced when the paperboard has been treated with a sizing agent. As only the paperboard edges are involved in this test, the internal sizing of the paperboard and also the type of fibre in use are of major importance.
The test sample is covered on both surfaces with a waterproof tape and cut to a specific size. The sample is then weighed before being placed in water at 80 °C, so that water can only be absorbed through the edges. After 20 minutes the sample is weighed again and the increase in weight recorded as the Wick test value in kg/m². This wicking test is used for testing of Solid Bleached Board products.
Surface water absorption, Cobb test
The Cobb value quantifies the amount of water absorbed via the paperboard surface during the Cobb test.
In the offset litho printing process, where water is used, there is a need for some degree of water holdout.
For packaging applications for deep freeze/ chilled foods the requirements can be demanding.
The paperboard sample is weighed and a cylinder with a cross sectional area of 1 dm² is placed on the sample. Water (100 ml) is poured into the cylinder. After 1 minute the cylinder is emptied and excess water blotted from the surface. The weight increase is registered as the one-minute Cobb value in g/m².
The test can be used for the outer surfaces as well as the internal layers of a multi-ply paperboard. The centre plies are tested after delamination of the outer plies.
Hard-sized Folding Box Board products, where the middle plies are additionally treated to give high water resistance for deep-freeze and chilled food applications, are tested using an extended time. The commonly specified time is 3 minutes, with the test also performed on the middle plies, in addition to the outer plies.
On pigment coated surfaces water absorption is to a large extent dependant on the coating composition. For uncoated surfaces internal sizing and composition of the surface size are important.
The internal sizing of fibres is of vital importance in slowing down the water absorption of the centre plies.