HK1074610B - Web packaging material for packaging food products - Google Patents

Description

Web-like packaging material for packaging food products

Technical Field

The present invention relates to a web-like material for packaging 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.

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 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, so as 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.

More specifically, the web of material has longitudinal fold lines forming the vertical edges of the package, and transverse fold lines forming the bottom edges of the package and also for folding the material along transverse seals.

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 height of the protuberances on the creasing rollers defines the depth of the fold lines and thus their crease strength, which is defined by a parameter commonly referred to as RCS (relative crease strength, which is the crease strength compared to a material without fold lines). The deeper the fold lines, the lower their crease strength and thus the lower the RCS.

Determining the depth of indentation is often a compromise between ease of forming the package and the contradictory requirements of achieving strength and stability of the final package.

That is, too deep a fold line makes formation easier, but can result in a weak or unstable package; conversely, shallower fold lines provide strength and stability, but the package is more difficult to form.

This problem is compounded by the fact that the fibres in the ply of material (hereinafter referred to as "paper" for simplicity) are generally oriented longitudinally, i.e. parallel to the direction of feed of the material on the machine, so that, for a given depth, the transverse fold lines have a lower RCS than the longitudinal fold lines, since the transverse indentations can damage the fibres of the paper.

Since the transverse fold lines are the fold lines that play a major role in the strength and stability of the package, the depth of the indentations should generally be determined in terms of transverse fold lines from a safety point of view, but at the expense of reduced ease of forming of the package.

DISCLOSURE OF THE 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 web of material for producing packages of food products and having a plurality of fold lines formed by creasing, the fold lines comprising a longitudinal fold line forming a vertical edge of the package, and a plurality of transverse fold lines forming a bottom edge of the package; characterized in that the longitudinal fold lines have a lower crease strength than the transverse fold lines.

The material according to the invention provides easy formability by means of weaker longitudinal folding lines, while giving the final package excellent structural properties by means of stronger folding lines forming the bottom edges of the package.

The conventional indentation also has the following problems.

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.

According to a preferred embodiment of the invention, the fold line is formed by compression creasing, having a concave profile on one surface of the material and a non-convex profile on the other surface.

Thus, creasing rollers having projections and counter rollers having smooth working surfaces, i.e. no pockets, which in conventional creasing act as "dies" for the projections on the other roller, may be used to form the fold lines. Therefore, the cost of the indentation apparatus can be significantly reduced.

Furthermore, since the material is indented by direct compression without being subjected to cutting action, problems and risks due to delamination are reduced.

Brief description of the drawings

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

fig. 1 schematically shows a machine for producing aseptic packages from a roll of web material according to the present invention;

fig. 2 shows a portion of a web packaging material according to the invention;

fig. 3 shows a schematic cross-section along the line III-III in fig. 2 illustrating the contour of a first fold line in the material shown in fig. 2;

fig. 4 shows a schematic cross-section along the line IV-IV in fig. 2 illustrating the profile of a second fold line in the material shown in fig. 2;

FIG. 5 shows a schematic cross-section of a step in a method of manufacturing a material for obtaining the fold line shown in FIG. 3;

FIG. 6 shows a schematic cross-section of a step in a method of manufacturing a material for obtaining the fold line shown in FIG. 4;

figure 7 shows a schematic cross-section of a step in a method of manufacturing a material for obtaining the folding line shown in figure 3, according to a variant of the invention;

fig. 8 shows a schematic cross section of a step in a method of manufacturing a material for obtaining the folding line shown in fig. 4 according to a variant of the invention.

Best Mode for Carrying Out The Invention

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

The roll 3 of material 2 comprises a plurality of folding lines, generally indicated by the reference numeral 4, and a printed decorative portion 5, which are repeated at intervals R equal to the length of paper 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.

Fold line 4 is formed by a creasing process and comprises a longitudinal fold line 4a forming a vertical edge of the finished package 17, and a transverse fold line 4b forming a bottom edge of the package 17.

According to the present invention, the crease strength of the longitudinal fold lines 4a is less than that of the transverse fold lines 4b, and this difference can be achieved by appropriately changing the crease depth as described in detail below.

The Relative Crease Strength (RCS) of the longitudinal fold line 4a, i.e. the ratio of the crease strength of the longitudinal fold line 4a to the crease strength of the material 2 without fold lines, should be in the range of 55% to 65%, preferably 65%; the RCS of line 4b should be in the range of 65% to 75%, preferably about 70%.

Therefore, the difference in RCS of the transverse fold line 4b and the longitudinal fold line 4a should be in the range of 2 to 20%, preferably 10%.

According to a preferred embodiment of the present invention, the fold lines 4a, 4b (fig. 5 and 6) are preferably formed by compression lines formed by a compression creasing process in which the material 2 is compressed between a creasing roller 20 and a smooth counter roller 22, the creasing roller 20 having a plurality of protrusions 21a, 21b corresponding to the compression lines 4, and the counter roller 22 having no recesses corresponding to the protrusions 21a, 21 b.

The outline of the rollers 20, 22 is shown partly and schematically in plan view in fig. 5 and 6, which clearly shows that the projections 21a have a greater height than the projections 21b to achieve the difference in the indentation strength of the lines 4a and 4 b.

This allows easy formation of the package while achieving good strength and stability.

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 acts on the opposite surface 25.

As clearly shown in fig. 3 and 4, compression lines 4a, 4b have a concave profile formed by a stepped side 26 on surface 23 of material 2 and a substantially flat or slightly concave profile on opposite surface 25.

Figures 7 and 8 show a variant embodiment of the invention in which the indentation is carried out using conventional methods.

In this case, the creasing is performed by two creasing rollers 30, 31 having respective working surfaces with precisely aligned projecting portions 32a, 32b and recessed portions 33a, 33b, respectively, thus locally producing double creasing of the material in a substantially U-shaped profile in cross-section. Also in this case, the indentation depth of the line 4a is greater than the indentation depth of the line 4 b.

Clearly, without departing from the scope defined by the appended claims. Variations may be made to material 2 as described herein.

Claims (7)

1. A web material (2) for producing packages (17) of food products and having a plurality of folding lines (4) formed by creasing, said folding lines comprising a longitudinal folding line (4a) forming a vertical edge of the package, and a plurality of transverse folding lines (4b) forming a bottom edge of the package (17); characterized in that the longitudinal fold line (4a) has a lower crease strength than the transverse fold line (4 b).

2. The material according to claim 1, characterized in that the difference between the relative crease strength of the transverse fold lines (4b) and the longitudinal fold lines (4a) is in the range of 2 to 20%.

3. The material according to claim 1 or 2, characterized in that the difference between the relative crease strength of the transverse fold lines (4b) and the longitudinal fold lines (4a) is 10%.

4. The material according to claim 2, characterized in that the longitudinal fold lines (4a) have a relative crease strength in the range of 55 to 65% and the transverse fold lines (4b) have a relative crease strength in the range of 65 to 75%.

5. A material as claimed in claim 1 or 2, characterized in that said fold line (4) is a compression line having a concave profile on a first surface (23) of said material (2) and a non-convex profile on a second surface (25) of said material (2).

6. A method of producing a web-like material (2) for packaging food products and having a plurality of folding lines (4), said method comprising a creasing step, wherein a web (3) of said material is compressed between first and second creasing rollers (20, 22; 30, 31) acting on opposite surfaces (23, 25) of said material (2); the first creasing roller (20; 30) having a first number of protruding portions (21 a; 32a) for creating a fold line (4a) longitudinally relative to the roll (3), and a second number of protruding portions (21 b; 32b) for creating a fold line (4b) transversely relative to the roll (3); characterized in that said first number of protruding portions (21 a; 32a) is higher than said second number of protruding portions (21 b; 32 b).

7. Method according to claim 6, characterized in that the second creasing roller (22) has a smooth working surface.