Compression-moulded tray and method of producing a fibre tray

Abstract

A compression-moulded tray of fibre material, said tray being formed of fibre material in a compression method, from a suspension of mechanical pulp of cellulose. The formed tray has been formed by press-drying using heat to a dry content of 80-95%, preferably 90-95%, and the fibre material of the formed tray has a density in the order of 400-650 kg / m3. The inside of the tray is provided with a protective barrier.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a compression-moulded tray of fibre material, said tray having an opening, an inside and an outside.BACKGROUND[0002]The handling of foodstuff put very high demands on the packaging. They must meet the hygienic requirements, i.e. bacteria and flavouring agents should not be able to migrate through the packages to and from the surrounding environment. In some cases the tray should even be gas tight, i.e. for chilled food for long storage or fresh meat in modified atmosphere. They should have enough strength to resist the handling during storage and transport. Tough environmental demands are also put on the packaging, i.a. as to recycling, composting or burning of used packages.[0003]It has become more and more common with ready-cooked food dishes, and in addition to serving as a package for storage of the foodstuff, there are also requirements that it should be possible to put the packages directly into a microwave oven or a...

AI Technical Summary

Benefits of technology

[0012]By choosing the mentioned kind of virgin fibre-based mechanical pulp of cellulose as fibre material in the tray, several advantages are obtained. Fibres of mechanical pulp are stiffer than any other type of cellulose pulp, such as chemical pulp or pulp that is partly or fully comprised of recycled fibre. This means that the tray formed from mechanical pulp is more resistant to deformation. The remaining residues of natural resins in the mechanical pulp also causes the formed tray to be self-hydrophobing, which is important in order for the tray to maintain its shape and strength even in humid environments. Press-drying also introduces built-in stress into the product which gives the rigidity at a low basis weight. Said stress is evenly distributed and results in an additional contribution to the stability, due to the fact that the fibres have been forced to a shape under heat and pressure into a fibre network, Inner stress yields in this case a better strength and stability. The hydrophobic fibres also prevent future penetration of water, which in turn also promotes long-lasting strength and stability.

[0013]The formed tray has been formed by dry-pressing under heat to a dry content of 80-95%, preferably to a dry content of 90-95%. This results in the forming of very strong hydrogen bonds between the individual fibres, and in the obtaining of a tray with high resistance to compressive stress.

[0014]Press-drying is preferably performed at 250-280° C. This temperature interval results in a good production efficiency. Higher temperatures may result in burning of the fibre material.

Problems solved by technology

The handling of foodstuff put very high demands on the packaging.

They must meet the hygienic requirements, i.e. bacteria and flavouring agents should not be able to migrate through the packages to and from the surrounding environment.

They resist conventional ovens, but the disadvantages are that they become very hot and sometimes even impossible to hold in your hands.

Aluminum forms are also very fragile and cannot resist a great load.

Moreover, they cannot be put in a microwave oven

An essential disadvantage with solid or foamed plastic trays is that they cannot be put in a conventional oven, since they will then melt.

The choice of material suggested in the U.S. patent for the forming pulp is however not optimal for the manufacturing process and results in a formed tray lacking in function.

Moreover, there is no specification of the pulp, only how the machinery works.

Also, the described manufacturing process and assembling have some flaws like low and uneconomical production rate, large areas that have to be well sealed against air leakage.

This results in bad reproducibility and a decreased quality of the trays.

The tools used may also cause crushing of cellulose at certain locations on the tray.

Even if the flexibility and elasticity have been improved, as is indicated in EP 1 160 379-A2, there are still limitations with regard to its flexibility and elasticity, which in turn results in limitations in the formability.

It is impossible to produce deep trays or multi compartment trays from a web, since it is impossible to form a tray or bowl from a flat sheet even if you have moistened it up to water a content 50%.

Furthermore, undesired folds are formed when depressions are made in the material web in connection with the forming of the trays.

The web used may even break.

An essential disadvantage with the trays according to EP 1 160 379-A2, is that the formed trays are stretched and that they have built-in tensions that may cause the formed trays to be deformed when exposed to stresses in the form of changes in temperature or when exposed to moisture or dampness.

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