METHOD AND SYSTEM FOR CONDITIONING A SHRINKABLE PLASTIC FILM

Abstract

 Method for conditioning a shrinkable plastic film; comprising providing a rewinding machine with an unwinding zone, a conditioning zone for a shrinkable plastic film and a rewinding zone; arranging a reel of shrinkable plastic film in the unwinding zone; mounting, in the conditioning zone, a conditioning roller provided with at least one row of punches; displacing the plastic film from the unwinding zone to the rewinding zone and generating in the plastic film, by means of the punches of the conditioning roller, rows of perforations forming tear lines; and determining a distance between consecutive rows of generated perforations, by means of the diameter of the conditioning roller and, when the roller comprises several rows of punches, by means of the number of said rows and the peripheral spacing between them.

Description

Technical field

[0001] The present invention relates to a method and a system for conditioning a shrinkable plastic film, applicable in the packaging sector, for the formation of shrink packages, in which said plastic film contracts over the outer surface of the product to be packaged by the application of heat.

Background

[0002] At present, the use of plastic films of different types to form a protective covering over a product or over a group of products is known; however, these plastic coverings have different characteristics and require the use of likewise different plastic materials.

[0003] A distinction should mainly be drawn between the coverings used in wrapping machines, the function of which is to keep the products to be wrapped grouped together, for example palletized loads, to allow their ventilation and to prevent the tear of said covering; and the coverings used in shrink-wrapping machines, the main function of which is to keep the products to be packaged grouped together and to provide additional protection thereto.

[0004] In wrapping machines, a combination is used of a stretchable plastic film, coming from a first reel, in which large windows are formed by punching and stretching for ventilation of the product to be wrapped, and reinforcing plastic cords formed by the lateral grouping of strips of plastic film obtained by longitudinal cuts from a second reel of plastic film and applied onto the stretchable plastic film.

[0005] In shrink-wrapping machines, a shrinkable plastic film is used which is arranged around the product and is contracted by the application of heat against the outer surface of the product in question. In this operation, the plastic acquires a high consistency, and it is advisable for the shrink-wrapped package to have tear lines in order to facilitate its manual tearing and the extraction of the product.

[0006] Application ES 2978509A1 describes a shrink package comprising: a first half, formed from a first shrink film provided with parallel rows of perforations affecting the entire width of said first film and forming tearable sections, and a second lower half formed by a second shrink film joined by welding to the first film; the obtained package comprising at least one tearable section.

[0007] The solution currently used to define said tear lines is the integration, in the packaging machine itself, of a device for perforating the plastic film.

[0008] Documents GB 1397709A, EP335480A1, EP1785257A1 and US 2014231493 describe packages formed from two reels of continuous film, in packaging machines that incorporate at least one perforating device which defines, in the continuous film coming from one of the reels, perforations that form, in the shrink package, tear lines or zones for tearing and opening the package.

[0009] Inside these packaging machines, the aforementioned shrink plastic films perform intermittent movements, advancing during the covering of the products to be packaged, and stopping during the welding of the two sheets on opposite sides of the shrink package.

[0010] The perforations in one of the plastic films may be made in an area comprised between the supply reel of said film and the package welding and cutting area, or else in the cutting area itself.

[0011] This operation gives rise to a series of drawbacks, among which mention may be made of: the risk of misalignment of the film or of stresses caused by the intermittent movements of the film, which could compromise the functionality of the film and the quality of the obtained package; the need to incorporate, in each packaging machine, the corresponding film-perforating device, with the consequent increase in the total cost of the packaging machine and in the complexity of its assembly, and the greater risk of breakdowns or maladjustments due to the incorporation of the perforating device in the packaging machine.

[0012] Likewise, various documents have been identified in the prior art that describe solutions related to the perforation or conditioning of sheet materials for packaging.

[0013] Document CN212196202U discloses a support for stretch film incorporating a needle roller intended to perforate the film before its application in wrapping processes. The system envisages that, after perforation, the film is subjected to stretching by means of rollers driven by gears, such that the holes can be enlarged in order to improve ventilation. Additionally, means are provided for generating ribs or longitudinal reinforcements in the perforated film. However, said solution falls within the treatment of stretch film integrated in wrapping equipment, without describing an independent conditioning process by rewinding, nor the generation of longitudinally spaced tear lines with a controlled periodicity.

[0014] For its part, document CN203832775U describes an automatic packaging and shrink-wrapping machine that integrates multiple functional modules, including a plastic film system with perforating elements. The perforation is carried out as part of a complex packaging apparatus that incorporates sealing mechanisms and a thermal shrink oven. However, the document does not contemplate a specific rewinding machine intended for the prior conditioning of shrink film by means of the controlled formation of transverse rows of perforations constituting lines of weakening or programmed tear.

[0015] Finally, document CN208828197U discloses an unwinding device for desiccant packaging paper incorporating a pressing roller provided with perforating needles in order to increase the permeability of the paper. It also includes lateral guiding means by means of grooved rollers to prevent deviations of the material during transport. However, the document relates to the treatment of paper and not to shrinkable plastic film, nor does it describe the geometric configuration of a conditioning roller that makes it possible to determine precisely the longitudinal distance between rows of perforations as a function of design parameters of the roller itself.

[0016] In view of the cited documents, it is found that the state of the art describes solutions relating to the perforation of sheet materials in different industrial contexts, whether in the treatment of stretch film integrated in wrapping machines, in complex packaging systems with sealing and shrink-wrapping, or in paper unwinding devices intended to improve permeability. However, none of said documents specifically addresses the technical problem consisting in providing an independent method and system for the prior conditioning of shrinkable plastic film by rewinding from reel to reel, capable of generating transverse rows of perforations configured as lines of weakening or controlled tear, with a predetermined and repeatable longitudinal distance between said rows, determined as a function of geometric parameters of the conditioning roller and suitable for the perimeter of the product to be wrapped.

[0017] Additionally, the known solutions do not contemplate the need for said conditioning to be carried out at high industrial production speeds, while simultaneously guaranteeing the stability of the material, the positioning precision of the perforations, and the uniformity of the longitudinal pitch between tear lines.

[0018] Consequently, there remains the technical need to develop a system that allows the controlled conditioning of shrink film, ensuring a precise periodicity of the lines of weakening and compatibility with high-speed industrial processes, without depending on the making of perforations in the wrapping or packaging machine itself.

Summary

[0019] The method for conditioning a plastic film, which is the subject matter of the invention, has technical characteristics aimed at satisfactorily solving the problem set out above.

[0020] Said method comprises the use of a high-speed rewinding machine, independent of the packaging machine, to condition a shrinkable plastic film intended for the manufacture of shrink packages or wrappings, by making rows of perforations in the plastic film and obtaining a reel of perforated shrinkable plastic film.

[0021] This solution not only avoids the incorporation, in each packaging machine, of a film-perforating device and the problems arising from such incorporation, but also provides an optimization that ensures greater speed, precision and reduction of possible defects in the perforation of the film, reducing the risks of misalignment or stresses that could compromise the functionality of the perforated film, especially in high-speed applications, where control of the film is critical to maintain the quality of the obtained package or wrapping.

[0022] Another object of the invention is to address specific technical challenges that are not resolved in the cited prior art and to provide benefits in terms of industrial production and functionality of the final product, which do not derive directly from existing methods.

[0023] Another object of the invention is that the reel of perforated film obtained by the method of the invention can be used in packaging machines intended to manufacture shrink packages, or in any other machine in the packaging sector that uses a shrinkable plastic film to form a package, covering, or grouping of various products; making it unnecessary for each of said machines to incorporate a specific perforating device, which entails a lower investment for companies having several packaging or wrapping machines.

[0024] The method comprises the continuous displacement of the plastic film from an unwinding zone to a rewinding zone, passing through a conditioning zone in which the film is perforated by means of a conditioning roller provided on its perimeter with at least one row of punches, and facing a counter-roller.

[0025] The displacement of the film can be carried out continuously and preferably at high speed, said speed being able to be comprised between 50 and 200 meters per minute, which makes it possible to perform the perforation under stable and uniform conditions.

[0026] According to the invention, the longitudinal distance between consecutive perforation lines generated in the film is determined by the geometric configuration of the conditioning roller.

[0027] In particular, said distance depends on the diameter of the conditioning roller and, when the roller comprises several rows of punches, additionally depends on the number of said rows and on the peripheral spacing between them.

[0028] By selecting the diameter of the roller and, where appropriate, the number and spacing of the rows of punches, a determined longitudinal periodicity of the perforations generated in the film can be obtained.

[0029] This configuration makes it possible to produce reels of previously perforated film whose distance between consecutive lines can be selected according to the perimeter of the product intended to be packaged, without the need to modify the packaging machine.

[0030] The method for conditioning a plastic film, specifically a shrinkable plastic film intended for the manufacture of shrink packages or wrappings, comprises the following steps:

• providing a rewinding machine independent of a packaging or wrapping machine, the rewinding machine comprising: an unwinding zone, a conditioning zone for a shrinkable plastic film, and a rewinding zone;
• arranging a reel of shrinkable plastic film to be conditioned in the unwinding zone;
• mounting, in the conditioning zone, a conditioning roller facing a counter-roller and provided, on its perimeter, with at least one row of punches;
• displacing the plastic film from the unwinding zone to the rewinding zone and generating, by means of the punches of the conditioning roller, rows of transverse perforations forming weakened tear lines or zones of the shrinkable plastic; and
• determining a distance, in the longitudinal direction of advance of the film, between consecutive rows of generated perforations, said distance being determined by the diameter of the conditioning roller and, when the roller comprises several rows of punches, by the number of said rows and the peripheral spacing between them.

[0031] The diameter of the conditioning roller and, where appropriate, the number and spacing of the rows of punches on the perimeter of the conditioning roller are selected according to the perimeter of the product intended to be packaged, such that the number of tear lines or zones included in the shrink-wrapped packages of different products can be limited, for example to two, independently of the size of the product to be packaged.

[0032] According to the method of the invention, the displacement of the shrinkable plastic film at high speed between the unwinding zone and the rewinding zone of the rewinding machine may be comprised between 50 and 200 meters/minute, which makes it possible to perform the conditioning of the film rapidly, precisely and without defects.

[0033] According to the invention, the system for conditioning a shrinkable plastic film intended for the manufacture of shrink packages or wrappings comprises:

• a rewinding machine provided with an unwinding zone, a conditioning zone and a rewinding zone for the shrinkable plastic film;
• a counter-roller arranged in the conditioning zone; and
• a conditioning roller mounted in the conditioning zone, facing the counter-roller, said conditioning roller being provided, on its perimeter, with at least one row of punches, and being configured such that the longitudinal distance between consecutive rows of perforations, forming tear lines in the shrinkable plastic film, is determined by the diameter of the conditioning roller and, when the roller comprises several rows of punches, is determined by the number and the peripheral spacing between said rows of punches.

[0034] The diameter of the conditioning roller and, where appropriate, the number and spacing of the rows of punches are configured to correspond to the perimeter of a product intended to be packaged.

[0035] The conditioning roller may comprise on its perimeter several rows of punches, individual or grouped, distributed on its perimeter with a uniform spacing, each row of punches, or each group of rows of punches, defining in the plastic film perforations forming weakened tear lines or zones, intended to facilitate the manual opening of the shrink packages formed with said plastic film.

[0036] The row or rows of punches may be arranged forming straight lines parallel to the geometric axis of the conditioning roller, defining in the plastic film rows of perforations perpendicular to the direction of displacement of the plastic film, or may be arranged forming helical lines on the conditioning roller to define in the plastic film rows of perforations oblique with respect to the direction of displacement of the plastic film.

[0037] According to the invention, the counter-roller is mounted on a fixed shaft, whereas the conditioning roller is mounted on a displaceable shaft, parallel to the fixed shaft of the counter-roller and connected to a linear actuator provided for its displacement in a direction perpendicular to said counter-roller, the system comprising an adjustable stop configured to limit the approach of the conditioning roller to the counter-roller.

[0038] This feature makes it possible to mount in the system conditioning rollers of different diameters and with a variable number of rows of punches or of groupings of rows of punches distributed and spaced by a variable measure on the contour of the conditioning roller; such that the weakened tear lines or zones defined by the alignments of perforations defined in the plastic film are suitably spaced to define, in the shrink packages formed with this plastic film, a determined number of weakened tear lines or zones, independently of the size of the product to be packaged; in any case guaranteeing that said shrink package includes at least one weakened line or zone of height and that the number of delicate tear lines or zones is small and is limited, for example to two or three, thereby avoiding an excessive weakening of the package.

Brief description of the drawings

[0039] To complement the description being provided and in order to facilitate the understanding of the characteristics of the invention, the present specification is accompanied by a set of drawings in which the following has been represented, by way of illustration and not of limitation:

• Figures 1 and 2 schematically show a plan view and an elevation view, sectioned by a vertical plane, of an embodiment example of the system for conditioning a shrinkable plastic film according to the method of the invention; the conditioning roller having rows of punches, forming groups of three rows, spaced apart and uniformly distributed on the contour of the conditioning roller.
• Figure 3 shows a perspective view of a reel of perforated plastic film, obtained with the system of the preceding figures.
• Figures 4 and 5 show a partial side view of the system of the invention, specifically of a lateral portion of the conditioning zone of the shrinkable plastic film, provided with a fixed shaft for mounting the counter-roller and with a displaceable shaft for mounting the conditioning roller, said system comprising in Figure 4 a conditioning roller of larger diameter with two rows of punches, individual and diametrically opposed; and in Figure 5 a conditioning roller of smaller diameter with four rows of individual punches and diametrically opposed in pairs.

Detailed description of embodiments

[0040] In the example shown in Figures 1 and 2, the system for conditioning a plastic film (5), specifically a shrinkable plastic film intended for the manufacture of shrink packages or wrappings, comprises a high-speed rewinding machine (1) provided with an unwinding zone (11) for the plastic film (5), a conditioning zone (12) for the plastic film (5), in which a perforated plastic film (51) provided with rows of perforations (52) is obtained, and a rewinding zone (13) for the perforated plastic film (51).

[0041] In the conditioning zone (12), a counter-roller (4) and a conditioning roller (3) parallel to and facing the counter-roller (4) are arranged.

[0042] In the example shown in Figure 1, the conditioning roller (3) comprises several parallel rows of punches (31) forming groups of three rows, distributed and spaced uniformly on the contour of the conditioning roller. Each group of rows of punches (31) defines in the plastic film a weakened zone of a suitable width to facilitate the gripping and tearing of any shrink package formed with said plastic film.

[0043] However, it should be mentioned that the rows of punches (31) may be individual, without forming groupings, as shown in Figures 4 and 5.

[0044] The rows of punches (31) define in the shrinkable plastic film (5), as it passes through the conditioning zone (12), rows of perforations (52) forming weakened tear lines or zones of the perforated plastic film (51), determined by the diameter of the conditioning roller (3) and by the number and spacing of the rows or groupings of rows of punches (31).

[0045] The perforated plastic film (51) is rewound into a reel (22) arranged in the rewinding zone (13) of the high-speed rewinding machine (1); and finally said reel (22) is unloaded from the rewinding machine (1) and stored until its use in any packaging or wrapping machine that uses shrinkable plastic film.

[0046] It has been envisaged that the rows of punches (31) may be parallel to the axis of the conditioning roller (3), as shown in the figures, or that they may be arranged forming helical lines on the conditioning roller (3), defining in the plastic film (5) rows of perforations oblique with respect to the direction of displacement of said plastic film.

[0047] Said rows of perforations (52), regardless of whether they are individual or form groupings as shown, for example, in Figure 3, define in the plastic film (5) weakened zones of tear, spaced along the same, and intended to facilitate the opening of a shrink package formed with said plastic film.

[0048] In the examples shown in Figures 4 and 5, the counter-roller (4) is mounted on a fixed shaft (41) and the conditioning roller (3) is mounted on a displaceable shaft (32) along guides (33); said displaceable shaft is parallel to the fixed shaft (41) and is connected to a linear actuator (6), represented in this case by a hydraulic cylinder, provided for its displacement in a direction perpendicular to the counter-roller (4); the system comprising an adjustable stop (7) configured to limit the approach of the conditioning roller (3) to the counter-roller (4).

[0049] In Figure 4, the use of a larger conditioning roller (3) and with two diametrically opposed rows of punches (31) makes it possible to define in the plastic film rows of perforations that are more widely spaced, said film thus being suitable for shrink packaging of a larger product, whereas the smaller conditioning roller (3) and with four rows of punches (31) makes it possible to define in the plastic film rows of perforations that are less widely spaced, the perforated plastic film thus being more suitable for shrink packaging of smaller products.

Claims

1. Method for conditioning a shrinkable plastic film intended for the manufacture of shrink packages or wrappings, characterized in that it comprises the steps of:

- providing a rewinding machine, independent of a packaging or wrapping machine, said rewinding machine comprising an unwinding zone, a conditioning zone for a shrinkable plastic film and a rewinding zone;

- arranging a reel of shrinkable plastic film to be conditioned in the unwinding zone;

- mounting, in the conditioning zone, a conditioning roller facing a counter-roller and provided, on its perimeter, with at least one row of punches;

- displacing the plastic film from the unwinding zone to the rewinding zone and generating, by means of the punches of the conditioning roller, rows of perforations transverse to the width of the film, forming tear lines in the shrinkable plastic film; and

- determining a distance, in the longitudinal direction of advance of the film, between consecutive rows of generated perforations, said distance being determined by the diameter of the conditioning roller and, when the roller comprises several rows of punches, by the number of said rows and the peripheral spacing between them.

2. Method according to claim 1, wherein the diameter of the conditioning roller and, where appropriate, the number and spacing of the rows of punches on the perimeter of the conditioning roller are selected according to the perimeter of the product intended to be packaged.

3. Method according to any one of the preceding claims, wherein the displacement of the shrinkable plastic film between the unwinding zone and the rewinding zone is carried out continuously.

4. Method according to claim 3, wherein the continuous displacement of the shrinkable plastic film is carried out at a speed comprised between 50 and 200 meters per minute.

5. System for conditioning a shrinkable plastic film intended for the manufacture of shrink packages or wrappings, characterized in that it comprises:

- a rewinding machine (1) provided with an unwinding zone (11), a conditioning zone (12) and a rewinding zone (13) for a plastic film (5);

- a counter-roller (4) arranged in the conditioning zone (12); and

- a conditioning roller (3) mounted in the conditioning zone (12), facing the counter-roller (4), said conditioning roller being provided, on its perimeter, with at least one row of punches (31), and being configured such that the longitudinal distance between consecutive the rows of perforations (52), forming tear lines in the perforated plastic film (51), is determined by the diameter of the conditioning roller (3) and, when the roller comprises several rows of punches (31), is determined by the number and the peripheral spacing between said rows of punches (31).

6. System according to claim 5, wherein the diameter of the conditioning roller (3) and, where appropriate, the number and spacing of the rows of punches (31) are configured to correspond to the perimeter of a product intended to be packaged.

7. System according to any one of claims 5 or 6, wherein the conditioning roller (3) comprises on its perimeter several rows of punches (31), individual or grouped, distributed on its perimeter with a uniform spacing,

8. System according to any one of claims 5 to 7, wherein the row or rows of punches (31) are arranged forming straight lines parallel to the geometric axis of the conditioning roller (3) and define in the plastic film (5) rows of perforations perpendicular to the direction of displacement of the plastic film (5).

9. System according to any one of claims 5 to 7, wherein the row or rows of punches (31) are arranged forming helical lines on the conditioning roller (3), defining in the plastic film (5) rows of perforations oblique with respect to the direction of displacement of the plastic film (5).

10. System according to any one of the preceding claims, wherein the counter-roller (4) is mounted on a fixed shaft (41) and the conditioning roller (3) is mounted on a displaceable shaft (32), parallel to the fixed shaft (41) and connected to a linear actuator (6) provided for its displacement in a direction perpendicular to the counter-roller (4), the system comprising an adjustable stop (7) configured to limit the approach of the conditioning roller (3) to the counter-roller (4).

Drawing