Classification and designs for packaging
There are many different types of package in use throughout the world (see Annex I), many of which have been carefully evaluated with respect to produce and market system, while other types have often been adopted for general use without thorough evaluation. Changes to improve such packages are still required. Some different types of package include:
1. Sacks: flexible, made of plastic or jute.
- bags: small size sack
- nets: sacks made of open mesh
2. Wooden crates.
3. Carton or fibreboard boxes.
4. Plastic crates.
5. Pallet boxes and shipping containers.
6. Baskets: made of woven strips of leaves, bamboo, plastic, etc.
Sacks and nets
The materials used for sacks and nets may be woven natural fibre (jute, kenaf, sisal, cotton), woven synthetic (polypropylene, polyethylene), knitted natural fabric (cotton), knitted synthetic (polyethylene) or non-woven synthetic (propylene).
FIG.1. Sacks and nets
Advantages and disadvantages of sacks and nets.
The advantages of using sacks and nets are merely financial. The sacks and nets are cheap, have a low weight/volume ratio and, if made of a synthetic material, will not rot.
The disadvantages include a low protection against puncturing, compression, vibration and impact injuries such as dropping, difficult stacking, a low rate of vapour transmission and the need of special stitching equipment.
In general, nets are only suitable for hard produce such as coconuts and root crops (potatoes, onions).
Advantages and disadvantages
Commonly used are wirebound crates for citrus/potatoes, wooden trays for tomatoes and wooden field crates.
The advantages of wooden crates are:
- The crates can be manufactured and repaired locally.
- Wood is relatively resistant to different weather conditions and (sea)water.
- Wooden crates are often used on more than one journey and have a higher efficiency for larger fruits, e.g. watermelons.
- Most crates have good ventilation and fast pre-cooling is possible.
Disadvantages of wooden crates are:
- Untreated wood can easily become contaminated with fungi and bacteria.
- Treatment of wooden crates with paint or other chemicals may cause produce deterioration.
- The material may be too hard or rough for produce like soft fruits, and therefore liners of a soft material may be needed.
- Disposal of the crates after use.
- Manufacturing of wooden crates puts an extra claim on the natural forest resources.
A wooden crate consists of rigid corners with planks nailed or stretched against those corners. Plank thickness varies normally between 3 and 8 mm. Cutting the wood will result in loss due to the saw thickness (2-3 mm). A slicing machine can be used for thin planks up to 6 mm but these machines are expensive. There are several different constructions possible for wooden crates:
a. Nailed crates: (e.g. apple or pear crate ,field crate)
FIG.1. Nailed crates
Nailed crates are rigid and strong boxes which serve as multi-trip containers with a long life time.
The planks have a thickness of at least 6 mm. Because of the rigidity the crate is quite heavy and the initial cost is high compared to, for instance, wirebound crates. Spacing between the planks, (bottom, sides) and/or between top side plank and the bottom of the next crate creates is recommended for good ventilation.
Nailed crates are frequently used for domestic transport e.g. as a field crate or as a crate to transport produce from the producer to the wholesaler or trader.
Water has no direct influence on the strength of the crate, but rot will. An advantage of nailed crates is the possibility to repair the crate.
Disadvantages of the rigid nailed crate include the high return freight volume. A partial solution to this problem is to put one crate in two other crates which are placed opposite each other; so three empty crates will take up the space of two stacked crates.
b. Stitched crates: (tomato)
FIG.1. Stitched crates
Stitched crates are made of thin (3-4 mm) pieces of wood stitched together. Corner pieces, mostly triangular, provide the necessary strength to stack crates. This type of crate is mainly used for single journeys.
c. Wirebound crates: (orange crate, grapefruit crate, potato crate)
FIG.2. Wirebound crates
As a rigid, cheap crate with a good stacking strength it is mainly used for single journeys. Wirebound crates are stitched crates with a wire under the stitches which gives extra strength to the container. The wire also serves as a hinge and as a lock for the lid. These crates provide good ventilation and fast pre-cooling is possible. The price of these crates is low (around US$ 1.10 FOB and US$ 1.80 CIF St. Vincent).
Using them carefully, wirebound crates are capable of sustaining several journeys, which is proven by the (re-)use of Dutch wirebound potato crates in the inter-island trade.
d. Wooden collapsible crate (TDRI):
A wooden crate was designed by the Tropical Development and Research Institute (TDRI) for the huckster trade from Dominica. It consists of a removable top and bottom part and the crate can be folded using the hinges on the corners. The crate performed well in trials and it was possible to make up to twelve trips to other islands using the same crate. The price in 1987 was around US$ 8.00.
A more detailed description of this crate is given in
FIG.3. Fibreboard boxes
Fibreboard boxes are frequently used because of their low weight, their range of sizes and shapes and their availability.
a. Solid fibreboard boxes (cartons): have a thickness between 0.85 and 3 mm. If treated with wax these boxes are reasonably moisture resistant. The boxes are used for tomato, cucumber and ginger transport. Most of them are printed with attractive colours, a brand name and a label. The information can be stamped on this label after filling the box.
b. Corrugated fibreboard boxes: have a thickness varying from 1.2 up to 8 mm. The strength of corrugated fibreboard is determined by the type of fluting material, the type of facing material and its thickness and a single or double wall. Fluting and facings are kept in place by water resistant glue.
FIG.4. Corrugated fibreboard boxes
New box designs are usually tested for bursting strength, puncture strength, flat crush strength and edge crush (stacking) strength and it is advisable to use only such tested designs.
Advantages and disadvantages
Advantages of fibreboard boxes:
- Low weight and easy to handle.
- The relatively soft walls have a cushioning effect.
- The box can have any design, although it is recommended to use sizes fitting on the standard design of pallets.
- The boxes are delivered flat and assembling boxes can be done locally.
- The box has a low purchase cost.
- The material can be printed to give the box a pleasant and recognisable appearance. Also the label can be included in this print.
Disadvantages of fibreboard boxes:
- Moisture and high humidity can seriously weaken the box. Washed produce should be dried before putting it into the box. Empty boxes should be stored in a dry place preferably flat on top of pallets and not for long periods of time. For certain commodities waxed carton boxes are preferred.
- The low rigidity causes the stacking strength to be lower than for wooden or plastic crates. The fibreboard boxes are easily damaged by rough handling and ropes and too much weight on top of the box can crush the perishable produce inside.
- Ventilation holes are usually small, because large holes would seriously influence the strength of the box. It is advised that the hole surfaces are at least 5 percent of the total box surface. Decreasing the size of the holes by not properly closing telescope boxes or not properly stacking the boxes will decrease heat exchange, resulting in higher temperatures of the produce and increased spoilage. Vertical oblong slots, instead of round holes, have the advantage that the hole stays partly open even when the telescope box lid is not completely closed.
- The boxes are not re-usable.
In general, plastic crates are more expensive than wooden crates or carton boxes, but as a result of their longer life span the running costs are relatively low. Of course the possibility of pilferage of the crates should be taken into account when considering purchase of this type of packaging.
The hard surfaces have no cushioning effect, but, on the other hand, a hard, smooth surface is easy to clean and gives good protection to the produce.
Plastic crates are usually made of high density polyethylene (HDPE) or polypropylene (PP). Polyethylene has a higher impact strength and a low degradation by ultra-violet radiation while polypropylene has a better scratch resistance. The performance of both materials can be improved by adding anti-oxidants and UV protectants (for sunlight protection).
Advantages and disadvantages
Advantages of plastic crates:
- As a strong, rigid crate these plastic crates can be used for many journeys, making the cost per journey relatively low (Chapter 6).
- Different sizes and shapes are available to suit different customers needs. Colours can be used for marketing purposes.
- The containers are easy to clean and to disinfect.
- Plastic crates are strong and weather resistant and, because of their water resistance, the containers can be used in humid areas and during hydro-cooling.
Disadvantages of plastic crates:
- The hard surfaces can damage the produce and it is advised to use liners.
- The high purchase cost combined with the risk of pilferage could make this type of crate a financial risk.
- These crates generally have to be imported.
- Because this crate can be used several times, the extra cost for the return trip should be included in the total running cost.
- The loss of space (40-80 mm on the sides and around 10 mm from the height).
Plastic crates can have a stacking, a stack-nest or a collapsible design, the differences being particularly important when the crate is transported empty, since the volume determines the price to be paid for transport.
Collapsible plastic crates are the most expensive crates to purchase followed by stack-nest plastic crates and then the stacking crates. Prices F.O.B. in 1987 for a plastic crate with a size of 600 x 400 x 300 mm were respectively around US$ 25.-, US$ 13.- and US$ 11.-. It should be mentioned here that a similar size stacking crate can be purchased in Venezuela for approximately F.O.B. US$ 5.20 (1988 price).
a. Stacking crates
Because of the squared design with only the corner slightly rounded, an efficient use of available space is possible. Depending on the size of the crate, the loss of loading space compared with loose break bulk is between 20 and 30 percent.
Although stacking crates have a rigid design, some space during the return trip can be gained by putting one crate inside two others (see also wooden crates) and in order to overlap crates during stacking some space gaps in the rim of the crate are needed.
b. Stack-nest crates
FIG.1. Stack-nest crates
i. Stack-nest crate with swing bars Because of its vertically tapered shape the inside volume of a stack-nest crate is less than that of a crate with a squared design. Effective loading space is 5080 percent depending on the size of the crate. With the swing bar design five nested crates will use up the space of two stacked crates of the same size. If the bars are swung out the crates can be nested. A swing bar (9 mm) is swung from the outside or from the side over the top of the crate and forming a support for the following crate. The stack-nest crate is slightly weaker than the stack crate, because the bar is not resting on the corners (the strongest part of the crate) but on the long side of the crate. The swing bar is placed 1 to 2 cm under the rim of the crate and stacking is therefore easy. The crate on top should be placed within this rim. Sometimes a provision is made on the bottom side of the crate for the swine bar to fit in.
ii. Stack-nest crate with cover.
FIG.2. Stack-nest crate with cover.
Instead of the swing bar, the crate is closed by two cover parts on top of which the next crate can be stacked. An advantage is that this cover can be sealed, preventing pilferage of produce. The crates with cover are up to 50 percent more expensive than the ones without a cover.
iii. 180° stack-nest crate.
FIG.3. 180° stack-nest crate.
By making supports at several places inside the box, the box can be stacked and in a 180 degrees turned position be nested. These supports require extra space and dirt will assemble in the corners created by the supports.
c. Collapsible crates
A collapsible crate consists of a base with sides attached to it by plastic or metal hinges. Despite the saving of space when folded and their attractive design, this crate is generally not accepted in trade, most likely because of the high purchase cost.
Where conditions like the size of the field, the method of harvesting, the level of processing and packaging and the commodity allow better transport and storage, a higher efficiency can be reached by using pallet boxes.
Pallet boxes have the standard floor size of a pallet (1200 x 1000 mm)and, depending on the commodity, have standard heights.
Advantages of a pallet box system:
- Less manual handling and thus reduced cost in loading, filling and unloading (e.g. citrus harvest).
- More efficient use of available storage as compared to smaller crates.
- Increased speed of mechanical harvest.
Disadvantages of a pallet box system:
- The return volume of most of the pallet boxes is the same as the full load.
- The system requires higher investments in fork-lift trucks, trailers and handling systems to empty the pallet box.
- Because of the larger volumes, the produce is more easily injured during filling and unloading and the top layers will have made more movements during transport than when packed in smaller boxes.
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