A PACKING MATERIAL

Abstract: A packing material, preferably in the form of a bag intended for packing potatoes and similar light-sensitive vegetable products, is provided with a combination of a light reflecting material and a light absorbing material in mutually adapted minimum amounts to provide effective light protection. The light protecting material (5, 8) is applied to the surface of the bag, there being preferably a transparent area (4).

Description: A packing material The present invention concerns a packing material, prefer- ably in the form of a bag, which is intended for packaging potatoes and similar light-sensitive vegetable products. Many vegetable products are light-sensitive and will be damaged or deteriorate in terms of quality in a short time if they are exposed to short-waved electric light, e.g. from fluorescent tubes, daylight og direct sunlight. The problem is particularly great with respect to. pota¬ toes, which rapidly turn green under the influence of ultraviolet rays ' , get a bitter taste and also involve a health hazard since the formed green colouring matter is toxic, and the potatoes will thus be unsaleable. Bags of strong paper yield a relatively good protection against irradiation, but have several drawbacks limiting their use. Paper bags are i jurous to the environment, and they give waste problems and require rather large amounts of energy in the production. Finally, paper is non-trans¬ parent, which prevents inspection of the article without opening the bag. It would be obvious to use bags of non- toxic and inexpensive plastics materials, such as poly¬ ethylene, polypropylene, but these materials are transpa¬ rent in their non-coloured state and provide no protection against UV light. To obtain effective light protection the plastics sheet would have to be dyed with large amounts of light absorbing colouring matters or be coated with a strong layer of a light reflecting metallic layer, such as of aluminium, which would make the package very expensive. The EP 209 002 discloses a packing material intended for wrapping light-sensitive photografic material. For this purpose it is necessary to obtain complete protection of the contents from any light influence. This has been ob¬ tained by using a laminate of several plastics sheets and an intermediate metallic layer. At least one of the plas- tics sheets is strongly dyed with a dark covering colour¬ ing matter or pigment. The known packing material thus described is very expensive because large amounts of light protecting materials have to be used. The material accoring to the mentioned European patent cannot be used in an economically defensible manner for production of bags for packaging so inexpensive vegetable products as potatoes. The present invention is based on the finding that both effective and inexpensive light protection of potatoes and similar vegetable products can be obtained by using a plastics sheet or a laminate of plastics sheets provided with a combination of light reflecting metal layers and one or more light absorbing substances in relatively small amounts or concentration. Thus, the invention concerns a packing material comprising one or more plastics sheets, at least one layer of a light reflecting material and at least one layer consisting of or containing a- light absorbing material, said packing ma¬ terial being characterized in that the light reflecting material is a metal layer applied to the surface of the plastics sheet or one of these with such a thickness or density that only a portion of the incident light is re¬ flected, and that the light absorbing material consists of one or more colouring matters applied to the surface of or incorporated in at least one of the plastics sheets in such an amount, depending upon the type of the colouring matter, that a considerable portion of the light which is not reflected by the metal layer is absorbed by the said colouring matter or matters. According to a preferred embodiment of the invention the packing material is shaped as a bag intended for packaging potatoes and similar light-sensitive vegetable products, one of the sides being provided with the light reflecting and light absorbing materials, while the other side is transparent or has transparent areas. Such a bag can be placed with the transparent side down¬ wardly and the light-protecting side upwardly or against the light and will thus provide full protection against light influences. E.g. a customer in a shop can pick up the bag and inspect the contents through the transparent side. The transparent area can expediently be provided as a win¬ dow, which just forms part of one side. The contents of the bag will thus be protected against light hitting the other side of the bag, the edges and the bottom. The present bag can be manufactured by means of traditio¬ nal machinery for sheet production. It is preferred first to apply the light absorbing material to the sheet or spe- cific areas of the sheet by printing, e.g. offset print¬ ing. Then the light reflecting material is applied either by printing or in another manner, such as by electrode sputtering if the light reflecting material is aluminium. The best light protection is obtained when the light re- fleeting materials are arranged outermost. As mentioned above, an essential feature of the invention resides in adapting the amounts of light absorbing and light reflecting materials, respectively, in such a manner as to provide a light protecting effect which is just suf¬ ficient with the least possible amount of material. De- pending upon the type of the light reflecting materials and the price of these a skilled person can, by simple experiments, find precisely the amount and the mutual pro¬ portion between light reflecting and light absorbing ma- terials which are optimum, i.e. offer sufficient light protection with the lowest possible costs. The light absorbing material may be a colouring matter soluble in the plastics material or a combination of seve- ral colouring matters, e.g. with absorption maximum in the various regions of the spectrum. The combination should also incorporate materials with absorption maximum in the ultraviolet light, e.g. in the region 300-400 nm, since this light is particularly dangerous for potatoes. Also carbon black is useful as light absorbing material. The light reflecting material is preferably aluminium, e.g. in the form of metal particles suspended in a binder. Instead of aluminium, silver might have been used, but this is not as economical as aluminium. The present packing material is described more fully below with reference to the drawing, in which fig. 1 is a side view of a bag provided with a transparent area, and fig. 2 shows the same bag seen from the opposite side. The bag shown in fig. 1 is made of a transparent plastics sheet, e.g. of biaxially stretched polyethylene. The sheet is bent around an edge 7 and welded in the bottom with a welding seam 3 and along the opposite edge likewise with a welding seam 1. This results in an opening 2. The bag is moreover provided with two layers of light protecting ma¬ terial 5, 8 by offset printing, viz. first a light absorb- ing colouring matter and on top of this a layer containing metallic aluminium pigment. An area on one side is kept free and forms a transparent window 4. The light protecting materials around the window 4 form a frame 8. The amount of the light absorbing colouring matter and of the light reflecting aluminium pigment, respectively, is adapted following experiments to provide the least possible amount offering the desired protection. Inscriptions 6, which may e.g. state the contents of the bag, company name and/or advertising indicia may be applied to the side 5 of the bag, which is completely co¬ vered by light protecting materials and is to face upward¬ ly or outwardly against the light. The bag might also be manufactured by extrusion in tubular shape. Then, a welding seam 3 in the bottom of the bag will suffice.

Claims: P a t e n C l a i m s 1. A packing material comprising one or more plastics sheets, at least one layer of a light reflecting material and at least one layer consisting of or containing a light absorbing material, c h a r a c t e r i z e d in that the light reflecting material is a metal layer applied to the surface of the plastics sheet or one of these with such a thickness or density that just a portion of the incident light is reflected, and that the light absorbing material consists of one or more colouring matters applied to the surface of or incorporated in at least one of the plastics sheets in such an amount, depending upon the type of the colouring matter, that a considerable portion of the light which is not reflected by the metal layer is absorbed by the said colouring matter or matters. 2. A packing material according to claim 1, c h a r a c - t e r i z e d in that it is shaped as a bag intended for packaging potatoes and similar light-sensitive vegetable products, one of the sides being provided with the light reflecting and light absorbing materials, the other side being transparent or having transparent areas. 3. A packing material according to claim 1 or 2, c h a ¬ r a c t e r i z e d in that the metal layer is applied on top of the colouring matter or matters on the plastics sheets. 4. A packing material according to the preceding claims, c h a r a c t e r i z e d in that the light reflecting material is a metal layer, preferably aluminium.

Inventors: CHRISTIANSEN HENNING, CHRISTIANSEN, HENNING
Applicants: CHRISTIANSEN HENNING, CHRISTIANSEN, HENNING
Application year: 1990
Main classification: B65D30
IPC codes: B65D81