HK1074611B - Packaging sheet material for packaging pourable food products - Google Patents

Description

Packaging sheet for packaging pourable food products

Technical Field

The present invention relates to a packaging sheet for packaging pourable food products.

Background

A variety of materials are known for packaging pourable food products such as fruit juice, wine, tomato sauce, pasteurized or long-shelf (UHT) milk, etc.

Such packages are formed from a continuous roll-fed web of packaging material that may be slit to form blanks, or sealed longitudinally to form a tube of packaging material.

The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal material, such as polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of barrier material, formed, for example, by an aluminium film laminated to a layer of heat-seal plastic material, which in turn is covered with another layer of heat-seal plastic material eventually forming the inner face of the package contacting the food product.

According to one well-known technique, in order to produce aseptic packages, a web of packaging material is unwound from a reel and conveyed through a sterilizing chamber, in which the web is sterilized, for example by applying a sterilizing agent such as hydrogen peroxide, which is evaporated after sterilization, for example by heating and/or by applying radiation of a suitable wavelength and intensity to the packaging material.

The sterilized web of material is then folded into a cylinder and sealed longitudinally to form a continuous, vertical and longitudinally sealed tube in a known manner. In other words, the tube of packaging material forms an extension of the aseptic chamber and is continuously filled with the pourable food product and then fed into a form-and-seal unit for forming the individual packages, the tube being gripped and transversely sealed by means of pairs of jaws to form pillow packs (pillow packs).

The pillow packs are then separated by cutting the sealed portions between them and are conveyed to a final folding station where they are mechanically folded into the shape of the final package.

The package is formed by folding the packaging material along fold lines "creased" in the material. The creasing is performed by means of two creasing rollers having respective working surfaces with raised and lowered lines, respectively, which are precisely aligned to produce local deformations of the material, resulting in a substantially U-shaped cross-section, and with substantially no variation in the thickness of the material. The creased packaging material partially elastically returns to its original shape, so that the permanent fold line in the material is shallower than when creased, and has a concave profile on one surface of the material, typically the surface facing the outside of the package, and a convex profile on the opposite surface.

Conventional indentations have several disadvantages.

Firstly, the equipment required is very expensive, since the working surfaces for producing the creasing rollers need to be highly accurate to ensure that they match accurately and without damaging the material.

Secondly, when the material is folded along fold lines to form a package, the material may delaminate locally.

Another problem of the known creasing method is as follows:

although the formation of the packages must be matched to the fold lines, the feeding of the packaging material on the forming machine is generally controlled according to register marks printed on the material.

The reason for this is that conventional direct optical detection of fold lines still presents problems and no satisfactory solution has been proposed so far.

The indentation and printing are performed at different stages in the material production cycle, so that alignment errors between the two are unavoidable. Therefore, using the printed alignment mark as a positional reference for an operation that should be matched with the folding line inevitably leads to an error.

When printing is performed using any known printing technique, the packaging material is compressed between a printing cylinder and an opposing cylinder. If conventional creasing methods are used, the convex profile of the crease on the opposite cylinder side generates a pushing force, resulting in an unexpected and undesired contact between the packaging material and the printing cylinder on the concave side of the crease line, which results in a line with a blurred profile, which to a large extent results in an inability to perform optical detection.

Disclosure of Invention

It is an object of the present invention to provide a packaging material which does not have the above-mentioned disadvantages normally associated with known materials.

According to the present invention, there is provided a packaging sheet for packaging a pourable food product, having: a plurality of fold lines, the fold lines being compression lines having a concave profile on a first surface of the sheet and a non-convex profile on a second surface of the sheet; at least one optically detectable alignment mark on the first surface, the alignment mark being formed at least in part by a compressed line; a decorative portion printed on the first surface; characterized in that the decorative part comprises at least one printed area which at least partially surrounds the compression line and in contrast therewith forms the register marking.

According to the invention, the fold line can be formed by a creasing roller with protuberances and a counter roller with a smooth working surface, i.e. without recesses, which in conventional creasing act as a "mould" for the protuberances on the other roller. Therefore, the cost of the indentation apparatus can be significantly reduced.

However, since the material is indented by direct compression without being cut, problems and dangers caused by delamination are reduced.

Compression creasing enables a sharper compression line to be obtained than with known creasing methods, which can be optically detected and thus can be used as an alignment mark.

On the other hand, the compression creasing also produces a flat or slightly concave profile on the surface of the packaging material in contact with the counter-roller, eliminating the thrust, and the concave opposite side of the fold line is absolutely free of ink, thus obtaining a high-contrast mark that can be ideally detected by an optical sensor.

Further according to the present invention there is provided a method of producing a sheet for packaging food products and having a plurality of fold lines, the method comprising a compression creasing step in which the sheet is compressed between a creasing roller acting on a first surface of the sheet and having a plurality of projections to produce fold lines in the form of compression lines and a substantially smooth counter roller acting on a second surface of the sheet, the method further comprising a printing step of printing a decorative portion on the first surface of the sheet, characterised in that the printing step produces a printed area which surrounds at least a portion of the compression lines so as to form an optically detectable register mark.

Drawings

Some non-limiting embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

figure 1 shows schematically a machine for producing aseptic packages from a roll of sheet material according to the present invention;

FIG. 2 shows a portion of a sheet packaging material according to the invention;

FIGS. 3 and 4 schematically illustrate various steps in a method of producing the material of FIG. 2;

fig. 5 shows a portion of a packaging material according to another embodiment of the invention.

Detailed Description

Number 1 in fig. 2 indicates a portion of sheet packaging material 2 provided in the form of a continuous roll 3.

The roll 3 of material 2 comprises a plurality of folding lines 4 and printed decorative portions 5, which are repeated at intervals R equal to the length of material required to produce a package.

The roll 3 may be used on a machine 6 for producing aseptic packages, as schematically shown in figure 1, the roll 3 being unwound from a reel 7, conveyed through a sterilization chamber (not shown) in which sterilization takes place and an assembly 8, the roll 3 being folded and longitudinally sealed by the assembly 8 to form a continuous vertical tube 9 in a known manner.

The tube 9 of packaging material is filled continuously with pourable food products by a known filling device 10, and the tube 9 is then conveyed to a form-transverse sealing station 14, where the tube 9 is clamped between pairs of jaws (not shown) which seal it transversely to form pillow packs 15.

Pillow packs 15 are then separated by cutting the sealed portions between pillow packs 15 and are conveyed into a final folding station 16, where pillow packs 15 are mechanically folded to form a final package 17.

The package is formed by folding the material along fold line 4 and controlling the feeding of the material by means of an optical sensor 16 which can "read" register marks 18 located on the material at the spacing R.

According to the present invention, the folding line 4 may be formed by a compression line formed by a compression creasing process (fig. 3).

More specifically, the material 2 is compressed between an creasing roller 20 and a smooth counter roller 22, the profile of creasing roller 20 being partly shown in plan view in fig. 3 and having a plurality of projections 21 corresponding to the compression lines 4, while the counter roller 22 has no pockets corresponding to the projections 21. The roller 20 suitably acts on the surface 23 of the material forming the outer surface of the package, i.e. on the surface on which the decorative portion 5 is printed, while the roller 22 should act on the opposite surface 25.

The height of the projections 21 ranges between 50% and 90% of the thickness of the material 2, preferably about 80% of the thickness of the material 2. The thickness of the material is reduced by the same percentage during compression, after which the material partially recovers, but retains a permanent compression set. The residual depth of the compression lines is suitably between 30% and 60% of the thickness of the material 2 and is equal to about 50% of the thickness of the material when a deformation of about 80% is produced during indentation.

As clearly shown in fig. 4, compression lines 4 have a concave profile formed by stepped sides 26 on surface 23 of material 2 and a substantially flat or slightly concave profile on opposite surface 25.

Figure 4 also shows schematically, in plan view, the profile of the printing roller 30 and of the counter-roller 31, which are in contact with the surfaces 23 and 25, respectively, of the material 2 at the compression line 4.

As fig. 4 clearly shows, the substantially flat or slightly concave profile of the compression line 4 on the side facing the counter-roller 31 eliminates the thrust on the material 2, which could cause the thinner portion of the material to come into contact with the printing roller 30.

The printing roller 30 is therefore only in contact with the surface of the material 2 outside the compression lines 4, thus presenting a clear "negative print" line on the material.

In a preferred embodiment of the invention, this property of the compressed indentation can be exploited to obtain optically detectable alignment marks that correspond exactly to the compressed lines 4. For example, with reference to fig. 1 and 2, the register mark 18 may be formed by a rectangular area 36 printed on the portion of material 2 that ultimately forms the bottom of the finished package 17. The zone 36 surrounds a portion of the compression line 4, so as to form, in contrast to the compression line 4, a broken, substantially Z-shaped "negative print" alignment line 37, which comprises a first portion 37a and a second portion 37b parallel to each other and perpendicular to the direction of feed of the web 3 on the machine 6, and a portion 37c inclined with respect to the portions 37a, 37 b.

Thus, as the web 3 is conveyed through the machine 6, the register marks 18 are detected by one or more optical sensors 16 for controlling the position of the web 3 at the various processing stations and connected to a processing-control unit 41 for controlling known means (not shown) for managing the position of the web 3.

With the Z-shaped register line 37 it is possible to control the position of the roll 3 in the feed direction and in the transverse direction in order to correct the transverse position of the still flat roll and thus to perform auxiliary operations such as cutting and applying removable tabs or opening mechanisms, or to correct the angular position of the tube 9.

In fact, the optical sensor 16 detects the first portion 37a, the inclined portion 37c and the second portion 37b of the alignment line continuously; the control unit 41 calculates a first time T1 between detection of the first portion 37a and the inclined portion 37c and a second time T2 between detection of the inclined portion 37c and the second portion 37 b; the lateral position error of roll 3 may be calculated and corrected based on the ratio of T1 and T2. More specifically, if sensor 16 is located on the mid-plane of alignment mark 18, i.e., in the correct or reference position of roll 3, then the correct lateral position of the roll of material corresponds to a ratio of T1 to T2 of 1. If the ratio is less than or greater than 1, the roll should be moved laterally in the appropriate direction in a known manner to reduce positional error.

In the variant shown in fig. 5, the register marking 18 is formed by compression lines 4, which compression lines 4 are formed only for registration purposes, i.e. it does not play a role in the formation of the package, the register marking 18 suitably comprising a square-shaped printed area 36, which encloses four compression lines 37d forming a square, and compression lines 37e along the diagonals of the square.

The mark can thus be "read" exactly in the same way as the zigzag alignment line 37, but because of the square shape, the mark can be read in two perpendicular material feed directions X, Y relative to the optical sensor 16.

This is useful, for example, in the case of the use of the marking 18 as an alignment mark on a unit for applying opening mechanisms to the finished packages 17, in which the packages are transferred forward in different orientations.

Clearly, changes may be made to material 2 as described herein without, however, departing from the scope as defined in the accompanying claims.

In particular, as an alternative or in addition to the marking 18, the material may be provided with an optically detectable register mark printed in a conventional manner, so that the material 2 can be used on conventional machines.

The marks 18 can also be read "directly", i.e. without a contrasting printed area.

Claims (9)

1. A packaging sheet (2) for packaging pourable food products, having:

a plurality of fold lines being compression lines (4) having a concave profile on a first surface of the sheet and a non-convex profile on a second surface of the sheet,

at least one optically detectable alignment mark (18) on the first surface (23), the alignment mark (18) being at least partially formed by the compression lines (4),

a decorative portion (5) printed on said first surface (23),

characterized in that said decorative portion (5) comprises at least one printed area (36) which at least partially surrounds said compression line (4) and forms said register mark (18) in contrast thereto.

2. The sheeting of claim 1, wherein the registration mark (18) comprises at least two parallel portions (37a, 37b) and an inclined portion (37c) between the parallel portions.

3. The sheet according to claim 2, wherein the alignment mark (18) comprises four portions (37d) arranged in a square and an inclined portion (37e) formed along a diagonal of the square.

4. A sheet according to claim 1, characterized in that the compression lines (4) are formed by steep sides (26) towards the first surface (23) of the sheet.

5. The sheet according to claim 1, characterized in that the depth of the compression lines (4) is in the range of 30 to 60% of the thickness of the sheet (2).

6. The sheet according to claim 1, characterized in that the depth of the compression lines (4) is equal to about 50% of the thickness of the sheet (2).

7. A method of producing a sheet (2) for packaging food products and having a plurality of fold lines, the method comprising a compression creasing step, wherein the sheet (2) is compressed between a creasing roller (20) and a substantially smooth counter roller (22), the creasing roller (20) acting on a first surface (23) of the sheet (2) and having a plurality of protrusions (21) to produce the fold lines in the form of compression lines (4), the counter roller (22) acting on a second surface (25) of the material, the method further comprising a printing step of printing a decorative portion (5) on the first surface (23) of the sheet (2),

characterized in that the printing step produces a printed area (36) which surrounds at least a portion (37) of the compression line (4) in order to form an optically detectable register mark (18).

8. Method according to claim 7, characterized in that the height of the protruding portions (21) of the creasing roller (20) is in the range of 50-90% of the thickness of the sheet (2).

9. Method according to claim 7, characterized in that the height of the protruding portions (21) of the creasing roller (20) is equal to 80% of the thickness of the sheet (2).