WO2000053417A1

WO2000053417A1 - Sheet, in particular for modular boxes, for transport of fruit and vegetables in general

Info

Publication number: WO2000053417A1
Application number: PCT/EP1999/001610
Authority: WO
Inventors: Gerlando Russo; Luigi Cattorini
Original assignee: DEITOMO SL; Costruzioni Meccaniche Luigi Bandera SpA
Current assignee: DEITOMO SL; Costruzioni Meccaniche Luigi Bandera SpA
Priority date: 1999-03-06
Filing date: 1999-03-06
Publication date: 2000-09-14
Anticipated expiration: 2001-09-06
Also published as: AU2932999A

Abstract

In order to obtain the best compromise between cost and strength according to use, the sheet (1) comprises two outer layers (3), which are made from unused homopolymer or copolymer polypropylene, or from mixtures of both, containing up to a maximum of 40% inorganic filler, and an inner layer (2), which is preferably made from recycled and/or new homopolymer or copolymer polypropylene, or from mixtures of both, containing 10 to 60% inorganic filler. As an alternative, the central layer can contain a mixture of organic and inorganic filler, in which the organic filler constitutes less than 40%.

Description

Sheet, in particular for modular boxes, for transport of fruit and vegetables in general

The subject of the present invention is a sheet, in particular for modular boxes, for transport of fruit and vegetables in general.,

As is known, boxes for fruit and vegetables in general must have relatively good mechanical characteristics, since, as the product transported contains a high percentage of water, it is relatively heavy, and, simultaneously, the cost must be as low as possible, since the boxes are often designed to be used on a single occasion. At present, a good compromise between strength and economy is achieved for example by boxes which are made from corrugated cardboard. However, these boxes have the disadvantage (which is particularly significant) that they lose the necessary mechanical characteristics if they are wetted.

The object of the present invention is thus to provide a sheet, in particular for production of boxes for fruit and vegetables in general, which is simultaneously a good compromise between the mechanical characteristics and the cost, and the mechanical characteristics of which, in particular, do not vary when the sheets are wetted, unlike the conventional sheets of corrugated cardboard.

These objectives are achieved by means of a sheet according to claim 1. Further characteristics are described in the dependent claims .

The structure is economical, owing mainly to use in the central layer of a mixture which consists of an inorganic filler, such as calcium carbonate, and of polypropylene, and is simultaneously strong and has an excellent finish externally, owing to the use of polypropylene which contains less than 10% inorganic filler.

The sheet thus consists of materials with characteristics which do not vary if they are wetted. The percentages indicated represent the range which best optimises the objectives according to the intended use, which, it is reiterated, involves production of modular boxes for transport of fruit and vegetables in general . The sheet as a whole can also be recycled, thus helping to reduce the environmental impact, and to reduce further the costs, since the material from which it is made is reusable.

The invention is illustrated by way of non-limiting example in the figures of the attached sheet of drawings, in which: figure 1 is a partial view in cross -section of a sheet according to the invention; figure 2 illustrates a partial view in cross-section of a cylinder for production of a sheet according to the invention; and figure 3 is a view according to the arrow III in figure 2.

With reference to the aforementioned figures, and in particular to figure 1, the sheet, which in particular is for modular boxes for transport of fruit and vegetables in general, and is generally indicated as 1, comprises an inner layer 2, and two co-extruded outer layers 3.

The two outer layers 3 are made from homopolymer or copolymer polypropylene, or from a mixture of^' both, with an inorganic filler which is unused, i.e. which is new, and not recycled. The inner layer 2 is made from recycled or new, homopolymer or copolymer polypropylene, or from a mixture of both, and from an inorganic filler, such as calcium carbonate, the latter being in a proportion which is variable from 10 to 60%.

It should be noted that as well as of calcium carbonate, the inorganic filler can consist of silicates, ground glass, ash etc. In addition, dyes and/or pigments can be included, such as carbon black, titanium dioxide etc, as well as other conventional additives.

As an alternative, the inner layer comprises a mixture of inorganic and organic filler, in which the content f organic filler is less than 40%.

The sheet 1 as a whole has a thickness of between 1 and 5 mm. In particular, the sheet which seems to be best for production of boxes for fruit and vegetables in general, is that which has the inner layer 2 made from 40-50% polypropylene, which may or may not be recycled, and from an inorganic filler such as calcium carbonate, with an overall thickness of between 1 and 2.5 mm.

For reasons of economy, the sheet 1 is obtained by means of at least two extruders, of which one extruder produces the two outer layers 3 , and the other extruder produces the inner layer 2. However the sheet 1 can also be obtained by means of three extruders, of which two extruders produce one each of the two outer layers 3, and the remaining extruder produces the inner layer 2. Each extruder 4 comprises a body 5 and one screw 6 (see figures 2 and 3) . In the example given, in its body 5, the extruder 4 has a pair of co-rotating screws 6, only one of which can be seen in figure 2, whereas both can be seen in figure 3. In the example given, the extruder 4 is preferably of the double-screw type, the screws 6 of which have a ratio of length to diameter of up to 42 D. The axes of the screws are indicated as 7, whereas that of the body 5 of the extruder is indicated as 8. The body 5 of the extruder 4 comprises, aligned along its axis 8, and listed in the direction of movement of the material (indicated by the arrow "F"), a main supply mouth 9, and a plurality of secondary supply mouths (in the example given, a first 10 and a second 11 secondary supply mouth), at least one venting mouth 12, and one outlet mouth 13, downstream from which there is disposed a die, which is not illustrated. Each screw 6 comprises a plurality of portions, which, listed in the direction of movement of the material (indicated by the arrow "F") are: a first decompressed transport portion 14, a first mixing-homogenisation portion 15, a second decompressed transport portion 16, a first compression portion 17, a second mixing-homogenisation portion 18, a third decompressed transport portion 19, a second compression portion 20, a third mixing-homogenisation portion 21, and a fourth decompressed transport portion 22. Each screw 6 is accommodated in the body 5, such that the initial sections of the first 14, the second 16, the third 19 and the fourth 22 transport portions are disposed perpendicularly relative to the vertical, respectively of the main supply mouth 9, the first and second secondary supply mouths 10 and 11, and the venting mouth 12. The remaining portions are positioned accordingly. The decompressed transport portions 14, 16, 19, 22 differ from the compression portions 17, 20, substantially in that the latter have a pitch which is smaller than the former. This configuration has proved to be particularly efficient for processing the aforementioned material, and in particular mixtures of polypropylene and inorganic filler in the form of calcium carbonate.

Claims

1. Sheet (1), in particular for modular boxes for transport of fruit and vegetables in general, comprising at least one inner layer (2) and two outer layers (3), which are co-extruded from a material based on polypropylene, characterised in that the two outer layers (3) are made from a mixture of unused polypropylene and from inorganic filler, and the inner layer (2) is made from a mixture of polypropylene and an inorganic filler, the said inorganic filler of the said inner layer being in a proportion which is variable from 10 to 60%.

2. Sheet according to claim 1, characterised in that the inner layer (2) is made both from the said inorganic filler and from less than 40% organic filler.

3. Sheet according to claim 1, characterised in that the outer layers (3) are made from homopolymer or copolymer polypropylene, or from mixtures of both, containing up to a maximum of 40% inorganic filler.

4. Sheet according to claim 1, characterised in that the said inorganic filler comprises calcium carbonate.

5. Sheet according to claim 1, characterised in that the said polypropylene is a homopolymer, or a copolymer, or a mixture of both.

6. Sheet according to claim 1, characterised in that it has a thickness of between 1 and 5 mm.

7. Sheet according to claim 1, characterised in that it has a thickness of between 1.5 and 2.5 mm.

8. Sheet according to claim 1, characterised in that it is obtained by means of at least two extruders (4) , of which one extruder produces the two outer layers (3), and the other extruder produces the inner layer (2) .

9. Sheet according to claim 1, characterised in that it is obtained by means of three extruders (4), of which two extruders (4) produce one each of the two outer layers (3) , and the other extruder produces the inner layer (2) .

10. Sheet according to claim 1, characterised in that it is obtained by means of extruders (4) , the body (5) of which comprises, aligned along its axis (8) , and listed in the direction of movement of the material (indicated by the arrow "F") , a main supply mouth (9) , a first (10) and a second (11) secondary supply mouth, at least one venting mouth (12) and an outlet mouth (13), downstream from which there is disposed a die, each screw (6) comprising a plurality of portions, which, listed in the direction of movement of the material, are: a first decompressed transport portion (14), a first mixing- homogenisation portion (15), a second decompressed transport portion (16) , a first compression portion (17) , a second mixing-homogenisation portion (18) , a third decompressed transport portion (19) , a second compression portion (20) , a third mixing-homogenisation portion (21) , and a fourth decompressed transport portion (22), each screw (6) being accommodated in the body (5), such that the initial sections of the first (14), the second (16), the third (19) and the fourth (22) transport portions are disposed perpendicularly relative to the vertical, respectively of the main supply mouth (9) , the first and second secondary supply mouths (10) and (11) , and the venting mouth (12), the remaining portions being positioned accordingly, the decompressed transport portions (14, 16, 19, 22) differing from the compression portions (17, 20), substantially in that the latter have a pitch which is smaller than the former.

11. Sheet according to claim 1, characterised in that each extruder is of the co-rotating double-screw (6) type.

12. Sheet according to claim 1, characterised in that it is obtained by means of extruders (4) which have screws (6) , the ratio of length to diameter of which is approximately up to 42 D.

13. Box for transport of fruit and vegetables in general, obtained from a sheet (1) according to one- or more of the preceding claims .