SECURITY SACK Field of the invention This invention relates to light-proof security sacks comprising at least one kraft paper ply and at least one ply impervious to light. The sacks can be used e. g. for storing and transporting materials which have to be protected from light.

Background of the invention Many materials need to be protected from light during storing, transport or handling. Such materials are e. g. light sensitive and photosensitive papers and films, many food products, and also many sensitive products of high technology.

In light-proof paper-based sacks, a black plastic film is usually used. Also papers with aluminium foils are used. One drawback of these materials is that they cannot be comfortably destroyed or recycled with paper material.

Summary of the invention The main object of the invention is to provide a paper sack which has good light- proof properties but which is also easy to recycle or destroy. The invention and some embodiments thereof are defined in the patent claims.

According to the invention, the sack comprises at least one kraft paper ply and at least one paper ply impregnated with carbon. The carbon impregnated ply provides imperviousness to light, and the kraft paper ply provides especially mechanical strength.

The sacks can be manufactured from paper webs by applying conventional techniques. The sacks can be used for the storing and transport of any goods which need to be protected from light or from unauthorised scanning.

Alternatively, the carbon impregnated paper ply can be used as part of a laminate comprising at least one paper layer and at least one carbon impregnated layer laminated on one of the paper layers. The ply may comprise e. g. paper layer and one carbon impregnated layer, or two paper layers and a carbon impregnated layer between them. The carbon impregnated ply may also be coated on one or both sides to form a carbon-cored ply. Carbon impregnated papers are commercially available.

The sack may comprise several kraft paper plies. The sack may comprise e. g. two kraft paper plies and a carbon impregnated ply or laminated paper ply between them.

The sack can be easily recycled, if desired. The carbon can be removed in a similar way as the carbon black of printing inks. The sack can also be easily burnt or composted with other paper waste, if desired.

The carbon laminated paper ply will also aid the dissipation of static electricity.

This will enable the sacks to be more safely used for materials which have a risk of self combustion due static discharge or which may be damaged by static electricity.

The carbon impregnated ply or laminate can be earthed by a suitable probe to equipments with sufficient conductivity. Such discharges may especially occur when the sacks are filled with powder or granular material.

The sack can be made permeable to air. This may be necessary e. g. when storing certain food products like vegetables.

The sack can also be made permeable to moisture. Thus water condensed inside the sack can be removed through the sack.

The sack can be scanned by security type X-ray equipment to prevent misuse.

The sacks will also have a tamper-evident feature as any attempt to gain access cannot be repaired or disguised, especially when the carbon impregnated paper ply is used as a lamination or a carbon-cored ply. This is an additional property that could assist on the proffered security. However these packing materials can be in certain circumstances too dense or light protection is not efficient enough; e. g. when storing vegetables a packing material must be at same time breathable and light proofing.

Brief description of the drawing Fig. 1 is a general view illustrating the security sack in accordance with this invention.

Description of the preferred embodiments Referring to the drawing, there is shown a general view of the security sack in accordance with this invention. The security sack of the embodiment of the present invention comprises of one kraft paper ply (1) and one carbon impregnated paper

ply (2). These two plies of paper are laminated together to form a light-proof and strong paper ply.

To manufacture the security sack according this invention, first the laminated paper ply is cut in a shape of a horizontal rectangle. This horizontal rectangle is then folded inwards along the vertical comer folds (3) and outwards along the vertical center folds (4). These vertical center folds (4) allow the security sack to be stored flat, and when the security sack is used, they allow the body of the security sack to expand in volume. After the folding of the vertical folds, the vertical edges of the laminated paper ply are joined together along the vertical seam (5) to form the body of the security sack. Vertical edges are joined together preferably with glue or other adhesive material.

After the body of the security sack is formed, the bottom of the security sack is formed by folding the bottom part of the body along the horizontal bottom fold (6).

The bottom fold (6) can consist of several horizontal folds to increase the durability of the security sack. After the folding of the bottom part, the lower horizontal edge of the body is joined together with the body of the sack along the horizontal seam (7) with glue or other adhesive material.

In the upper part of the security sack there is left an opening (8) for inserting objects in to the security sack. The edges of this opening can also be provided with glue or other adhesive material to ease the sealing of the security sack.

It is evident for one skilled in art that the present invention is not limited to the foregoing description, but includes that contained in the claims. For example the security sack of the present invention can vary in shape and in size. It can have several or none center folds and the bottom of the security sack can be formed by glueing the edges of the bottom part of the body together.