KR20120059519A - Polypropylene film comprising an opening aid - Google Patents

Abstract

The present invention relates to a biaxially stretched polypropylene film having a perforation line. The films have at least two perforation lines running parallel to each other and arranged at intervals of up to 10 mm. Perforation of the two lines is complementary to each other.

Description

POLYPROPYLENE FILM COMPRISING AN OPENING AID}

The present invention relates to a package made from a biaxially stretched polypropylene film having a perforation and a biaxially stretched polypropylene film having a perforation as an opening aid.

The success of biaxially stretched plastic films, especially films made from thermostatic polymers, in particular biaxially stretched polypropylene films, is inherently based on their excellent mechanical strength properties with relatively low weight, good barrier properties and good weldability. . The polyolefin film prevents the packaging contents from drying out quickly or losing fragrance with very little material input.

Consumer demand for hygienic, visually appealing, tightly sealed resistive packaging is inconsistent with the desire for easily controllable opening. The latter is a complaint of polyolefin film packaging among consumers and is considered a disadvantage compared to paper packaging.

Uniaxially stretched films exhibit a small tear resistance in the stretching direction, can be easily torn, and the tear can propagate. However, uniaxially stretched films cannot be used in many areas, in particular due to the lack of their mechanical properties in the transverse direction. Biaxial stretching, on the one hand, provides the desired high strength (moduli) in both dimensions; On the other hand, the preferred direction is thereby also equalized. As a result, in order to open a film package (eg a biscuit package), it must first be overcome with great force in order to tear the film. However, if the film is damaged or torn, the tear propagates out of control even with very little traction. These faulty use characteristics, including excessively large initial tear resistance combined with very low tear propagation resistance, reduce the acceptability of film packaging in the end-user market despite the advantages mentioned above.

In the state of the art, it has been proposed that such films having a predetermined breaking point should be provided. During opening, the film tears at this predetermined breaking point. However, these solutions make the films tear more easily, but because they do not actually help controlled tear propagation, such tears are often spread out of control.

A further known solution is to mechanically include predetermined breakpoints in the form of perforations or notches along the virtual open line. However, even this type of drilling does not guarantee controlled tearing. During opening, the tear only occurs first along the perforation line and then propagates in a randomly biased manner through the material.

This uncontrolled tear propagation behavior is a problem, particularly for biaxially stretched polypropylene films, because the tear propagation resistance of this material is particularly small. This problem particularly affects the packaging containing each item in a regular manner, without being loosely packaged, such as cigarettes, Weittabix, crispbreads, biscuit rolls and the like. These types of packaging particularly focus on the fact that consumers may wish to first separate only a single item and leave the rest in the package so that additional units can be separated later. Uncontrolled tear propagation in film packaging is particularly annoying for consumers in these applications.

International patent application publication WO 98/2312 describes packaging previously cut by a laser beam. This package exhibits a multilayer structure. In particular, a metallic intermediate layer is provided to prevent the laser beam from cutting through the film. This package is time-consuming and expensive due to lamination by the metal layer. This patent specification does not describe the exact design of the packaging at all.

In addition, the perforated film must exhibit adequate mechanical stability so that it can be used for the packaging of individual items. In the art, a method has been described in which perforation is integrated into the processing stage of a packaging process. This solution prevents any mechanical loads on the perforated film during, for example, rolling and unrolling. However, it is not possible to incorporate perforations in all packaging processes. On the one hand, the spatial conditions with existing plants often lead to simply no space for attaching this kind of device. Moreover, in the tobacco industry the packaging process is carried out at very high speeds which are too fast to puncture. Thus, it is not always possible to couple the film-piercing device to the plant used to pack a group of cigarette packs. However, the proper mechanical stability of the film conflicts with the simultaneous desire for easy opening packaging.

The problem addressed by the present invention involved providing improved packaging for organized individual items.

The problem underlying the present invention is solved by a packaging made from biaxially stretched polypropylene films containing individual items, wherein the films run parallel to each other and are located at least 10 mm apart at most 10 mm apart. Represent the perforation lines, and the perforations of the two lines are complementary to each other.

The above problem is further solved by a method of packaging individual items, which is used to wind the perforated film from a roll and to package individual items.

1 shows one embodiment of a film 2 having a circular perforation 1 having a length (diameter) B. The length of the gap between the perforations corresponds to the length A. Two perforation lines running in parallel are arranged at intervals C relative to each other. In the embodiment according to FIG. 1, the distance A is just as long as the length B of the perforation. The perforation lines are complementary to each other so that in each case the center of the perforation is in line with the center of the facing interval.
2 shows a film with circular perforations of length B greater than the length of the spacing A. FIG.
3 shows a perforation with a rectangular geometry, here again B> A.
4 shows a film with rhomboid perforations, such as produced by rotating knives, for example.
5 shows a film with elliptical perforation. Here again B> A.
6 shows the possible needle perforation geometry in which propeller-yang perforations are produced.
7 shows a film web showing several double perforations in the longitudinal direction.
8 shows the individual item packaging 3 which is opened by rupturing along the double perforation line 4.

A common feature of all these embodiments according to FIGS. 1 to 8 is that the spacing A between the perforations is only as large or smaller than the length B of the perforations themselves.

Two perforation lines that complement and run parallel to each other create a predetermined break point in the film, where the tear propagates in a very controlled manner after the initial tear. After tearing the opening, the tear proceeds in a controlled manner along one of the perforations or between two parallel perforations. The film package is only opened to the desired degree.

The packaging according to the invention is particularly suitable for aligned or stacked individual items, for example cigarette packs, and also for soft products such as butter, sausages and the like. This would allow the consumer to tear along the length of the film along a predetermined break point in such a way that the additional unit would not be blocked in the case of the individual item and would allow the individual item to be separated without falling off. Individual segments between parallel perforations are adjusted according to the size of the separate unit. This makes it possible to control whether one or more units can be easily separated by one opening.

Perforations can be applied to the film web in a suitable pattern. The line preferably runs in a straight line. However, the above line may also be applied using any geometry so that the predetermined break point corresponds to the shape and dimensions of the individual item packaged.

Perforations may be produced by mechanical perforation using a needle or knife, for example by a laser beam, or in some other manner, such that a continuous hole is created in the film. However, the perforations within the meaning of the present invention also have no continuous holes created in the film at that point, but correspondingly by removing the material simply by using a laser beam that penetrates only to a predetermined depth, for example. Represents a thin point that is made thinner at a point. In these embodiments, 10 to 80% of the original film thickness, preferably 20 to 60% of the original film thickness is maintained close to the thin point. As the packaging is thereby kept sealed, it continues to meet all sanitary conditions, and its barrier properties are not adversely affected.

In addition, holes, incisions or thin spots (perforation B) progress alternately along the perforation lines with the intact film areas, the length A of which is indicated by the perforation interval. Thus, the spacing within the meaning of the present invention is the area of the intact film from the end of one perforation to the beginning of the next perforation in the same perforation line.

The geometry of the perforation may vary and depends on the method of perforation. Needles or rotary knives can be used for drilling. In the case of perforations made of non-continuous thin points, laser or ultrasound is preferred. Needle perforation produces a round or oval or propeller-shaped form, which is produced by allowing the needle and the film to act during the perforation and move relative to each other. Knife perforation produces more rectangular or oblong incisions or thinner points. Laser and ultrasound methods produce different geometric shapes. Except in the case of circular drilling, all drillings have larger dimensions in one of the two basic directions (longitudinal) aligned along the perforation.

The perforations usually have a length B of 0.1-8 mm, preferably 0.3-6 mm, in particular 0.5-3 mm, in the longitudinal direction described above. The size of the perforations perpendicular to this longitudinal direction is correspondingly smaller and typically corresponds to 5 to 80%, preferably 10 to 50% of its dimensions in the longitudinal direction. This does not apply to circular drilling. Round and approximately round perforations have a diameter of 0.1-6 mm, preferably 0.3 to 5 mm, in which case the diameter corresponds to the length of perforation B.

Especially in the case of small tear forces, perforations with a length of> 1 to 6 mm are particularly preferred, in particular also lengths of 1.5 to 6 mm or 2 to 4 mm. Surprisingly, even these relatively large or long perforations do not adversely affect the mechanical strength of the film. These embodiments can also be very rolled up into film rolls and unfolded on the packaging machine without any difficulty.

The length A of the area, ie the intact film between the perforations, is 0.05 to <8 mm, preferably 1 to 6 mm. For embodiments with long perforations of 1.5 to 6 mm, intervals of> 4 to 10 mm are preferred, for example. The dimension of the interval A is selected in relation to the length B such that the length B of the perforation is at least as large or greater than the interval A. The length or diameter of the perforation is generally at least 10% greater than the length of the gap. The length A of the gap is generally 10 to 90%, preferably 20 to 85% of the length B of the perforation.

Dimensions indicated for puncturing and spacing also apply in the same way for puncturing in the form of discontinuous thin spots, some of which may likewise be circular, elliptical or elongated.

The dimension of the spacing between the perforations along the line is generally constant or only slightly varies in terms of typical production precision. In the same way, the size of each perforation along the line does not change or only slightly (10% or less), ie the diameter of the hole or the length of the perforation is for example constant. Likewise, the spacing between the perforations and the two parallel perforation lines has predetermined break points with approximately equal dimensions.

What is essential to the invention is that the predetermined breaking point provided is formed from two parallel running perforations arranged at intervals C of up to 10 mm. The spacing C of these two lines is preferably 0.5 to 8 mm, in particular 0.8 to 5 mm.

A second feature of the predetermined break point essential to the present invention is the configuration of the perforations in the two perforation lines running parallel to each other. The offset arrangement of the perforations in the two lines was found to lead to a surprising improvement in the control for tear propagation. In this complementary alignment, the perforation in the second line does not start at the same level as the opposing perforation in the first line. In this way, the perforation at the second line includes at least partly the spacing at the first perforation line. In a preferred embodiment, especially where the perforations are greater than the gap, the zone of one perforation line is completely covered by the perforation of the opposing lines.

In a preferred embodiment, the center of the zone of the first perforation line is in each case aligned with the center of the opposing perforation in the second perforation line so that a symmetrical pattern of perforation is produced.

Surprisingly, the alignment of two parallel perforation lines complementary to each other significantly improves the control of the tearing process. The present invention also shows that the individual items exhibit a corresponding mechanical stability, and if the individual items are aligned within the package in such a way that their edges run horizontally with the double line, the package breaks at a predetermined break point on the individual item's edges. You can do that.

Perforation lines are generally applied in the machine direction of the film. Perforation is combined at the same time as cutting the film into a narrower film width, whereby it can be performed in one working cycle. Alternatively, the perforation may be performed before or after cutting the film to the final width. In all these process variants, the perforated film can be fed, for example, on a roller with a suitable drilling tool, for example these rollers can be equipped with needles or knife blades. . In the case of laser or ultrasonic perforation, the corresponding tool is located above or below the film web. By these methods, the film to be perforated is unrolled, and after perforation is applied in accordance with the present invention, the perforated film is again curled, which is used in a plant for packing individual items, i. Used for packaging. Surprisingly, the above perforations do not affect the rolling behavior of the film or are only negligible so that the perforated film can be unfolded using conventional apparatus. It has also been surprisingly shown that the perforations according to the invention do not affect the mechanical stability of the film to the extent that tearing, cutting, thick points or elongation occur when the film is rolled out.

Rolls of perforated film are used to produce the packaging according to the invention. The packaging according to the invention is particularly suitable for individual items lined up or stacked and also for soft products such as butter, sausages and the like. The consumer will be able to tear the film to length along a predetermined break so that the individual item can be separated without the others falling out of control in the case of the individual item. Individual segments are adjusted according to the size of the unit being separated. This makes it possible to control whether one or several units can be conveniently disconnected after opening.

Biaxially stretched polypropylene films are generally used as the above films. Depending on the type of packaging, the film may be a translucent to transparent or opaque film. "Opaque film" in the sense of the present invention means a non-transparent film having a light transmittance (ASTM-D 1003-77) of up to 70%, preferably up to 50%. The film can in principle be monolayer or multilayer. Laminates are also suitable for packaging according to the invention; These are preferably formed from the films described in the present invention.

In the case of transparent embodiments, the formulation of the film and the type of laser can be adjusted relative to each other such that the laser beam leaves behind colored lines close to white or thinning. This means that the packaging will display an identifiable marking that shows where the consumer will proceed to tear to open the package for ease of handling.

Available thermoplastic composites for the film include polyolefins made from olefin monomers having 2 to 8 C-atoms. Particularly suitable are propylene polymers, ethylene polymers, butylene polymers, cyclo-olefin polymers or mixed polymers of propylene, ethylene, butylene units, or cyclo-olefins are suitable. The layers of the film or in the case of single-layer embodiments generally contain at least 50% by weight, preferably 70 to 99% by weight, in particular 90 to 98% by weight, of thermoplastic polymer in each case with respect to the weight of the layer. do.

Propylene polymers are preferred as polyolefins. These propylene polymers contain 90 to 100% by weight, preferably 95 to 100% by weight, in particular 98 to 100% by weight, melting points of 120 ° C. or higher, preferably 130 to 170 ° C., and generally Has a melt flow index of 0.5 g / 10 min to 15 g / 10 min, preferably 2 g / 10 min to 10 g / 10 min at a force of 230 ° C. and 21.6 N (DIN 53 735) . Isotactic propylene homopolymer with an atactic ratio of 15% by weight or less, copolymer of ethylene and propylene with an ethylene content of 10% or less, olefin content of 10% or less Copolymers of propylene with C ₄ -C ₈ olefins, terpolymers of propylene, ethylene and butylenes having an ethylene content of 10% by weight or less and a butylene content of 15% or less by weight of the core layer Preferred propylene polymers for which isotactic propylene homopolymers are particularly preferred. The weight percentages given relate to the individual polymers.

Also suitable are mixtures of the aforementioned propylene homopolymers and / or copolymers and / or terpolymers and other polyolefins, in particular polyolefins of monomers having 2 to 6 C-atoms, wherein the mixture is at least 50% by weight. %, In particular at least 75% by weight, of propylene polymers. Other suitable polyolefins in the polymer mixture are polyethylene, in particular HDPE, LDPE, VLDPE and LLDPE, wherein the proportion of polyolefins in each case does not exceed 15% by weight relative to the polymer mixture.

If desired, the layer of the film, preferably the base layer or the intermediate layer, may also contain pigments and / or vacuole-initiating particles in the respective amounts customary for the opaque embodiment. .

The film according to the invention may be a single layer, said film preferably being multilayer. To achieve this, one-sided or two-sided intermediate and / or top layers can be applied to the base layer. Thus, the multilayer embodiment of the film, if necessary, represents an intermediate layer and an upper layer in addition to the base layer.

These additional top and / or intermediate layers are generally made from polyolefins. They contain at least 70% by weight, preferably 75 to 100% by weight, in particular 90 to 98% by weight of polyolefin. The same polymers as above are in principle suitable for these further layers as described above for the base layer.

Suitable for the top layer are ethylene and propylene; Ethylene and butylene; Propylene and butylene; Ethylene and another olefin having 5 to 10 carbon atoms; Copolymers of propylene and another olefin having 5 to 10 carbon atoms, ethylene and propylene and butylene; Or a terpolymer of ethylene and propylene and another olefin having 5 to 10 carbon atoms, or a mixture or blend of two or more of the foregoing homo-, co- and terpolymers.

Especially preferred of these are in each case a statistical ethylene propylene copolymer having an ethylene content of 2 to 10% by weight, preferably 5 to 8% by weight relative to the total weight of the copolymer, or 4 to 25% by weight, preferably Is a statistical propylene-butylene-1-copolymer having a butylene content of 10 to 20% by weight, or in each case 1 to 10% by weight, preferably 2 to 6% by weight of ethylene content and 3 to 20 Statistical ethylene-propylene-butylene-1 terpolymers having a butylene-1 content of 8% to 10% by weight, or an ethylene content of 0.1 to 7% by weight relative to the total weight of each polymer blend, 50 Blends of ethylene-propylene-butylene-1 terpolymers and propylene-butylene-1 copolymers having a propylene content of from 90% by weight to butylene-1 content of 10-40% by weight.

The co- or terpolymers described above generally have a melt flow index of 1.5 to 30 g / 10 minutes, preferably 3 to 15 g / 10 minutes. Melting point is in the range of 120-140 degreeC. The above blends of co- and terpolymers have a melt flow index of 5 to 9 g / 10 minutes and a melting point of 120 to 150 ° C. All melt flow indices shown above are measured at 230 ° C. and a force of 21.6 N (DIN 53 735). The layer of co- and / or terpolymer preferably forms the top layer of the sealable embodiment of the film.

The total film thickness can vary within a wide range and depends on the application purpose. Preferred embodiments of the film have a total thickness of 5 to 250 μm, wherein 10 to 100 μm, preferably 20 to 80 μm.

In the sense of the present invention the base layer is a layer which accounts for at least 50% of the total film thickness. Its thickness derives from the difference between the total thickness and the thickness of the upper and middle layer (s) applied, and thus can vary within a wide range in a manner similar to the total thickness. The top layer forms the outermost layer of the film and is measured at 0.5 to 5 μm, preferably 1 to 3 μm. The intermediate layer is between 1 and 20 μm, preferably between 1 and 10 μm.

Also in order to further improve certain properties of the polypropylene film according to the invention, the base layer and also the intermediate layer (s) and the top layer (s) are in each case an additive, preferably anti-blocking, which is usually incompatible with an effective amount. Hydrocarbon resins and / or antistatic and / or anti-blocking agents and / or antifriction and / or stabilizers and / or which are compatible with the polymer of the core layer and the top layer (s) except for the agent. It may contain a neutralizing agent.

The film is produced according to extrusion methods known in the art. In view of this method, the melt corresponding to each layer of the film is extruded by a flat film extrusion die. The film obtained in this way is discharged for solidification on one or more roller (s) and cooled. The temperature of the discharge roller or rollers is 10 to 90 ° C, preferably 20 to 60 ° C.

Thereafter, the film is stretched biaxially. Biaxial stretching can be carried out simultaneously or continuously, in which continuous biaxial stretching, in which the film starts stretching longitudinally (in the machine direction) and then stretches laterally (perpendicular to the machine direction), is particularly preferred. Do. In the longitudinal direction, the stretching of the film is preferably 3: 1 to 7: 1 and takes place at a temperature of 140 ° C. or lower, preferably 125 to 135 ° C. In the transverse direction, stretching is preferably from 5: 1 to 12: 1 and is carried out at a temperature of at least 140 ° C, preferably of 145 to 160 ° C. The longitudinal stretching is advantageously carried out with the help of two high speed rollers running at different speeds depending on the desired stretching ratio, and the transverse stretching is carried out using the corresponding biaxial tenter. In principle the film can be stretched simultaneously in the longitudinal-transverse direction. These simultaneous stretching methods are known in the art.

The film is then held at a temperature of 110-150 ° C. for approximately 0.5-10 seconds for thermofixing (heat treatment). If desired, one or two surface (s) of the film can be corona- or flame-treated after biaxial stretching using one of the known methods.

If desired, the film may be laminated, coated, melt-coated, varnished or cladding using additional processing steps prior to production and perforation before imparting additional beneficial properties to the film. can do. Composites of polypropylene films and polyethylene films are particularly preferred as laminates. Composites of this nature can be produced by laminating each film. A further technically advantageous variant for the production of PP / PE laminates is extrusion-coating suitable polyethylene on biaxially stretched polypropylene films. Extrusion coatings of this kind are known in the art. Laminates made from PP / PE films are advantageous when treated with a laser beam and have been found to be less easy to accidentally perforate.

The packaging according to the invention is characterized by controllable tear properties. If necessary, the force required to start tearing at the rim of the film can be reduced by using a notch, preferably a V-shaped notch. Pavement tears can propagate significantly more easily and with greater control. In addition, the packaging still exhibits all the advantages exhibited by conventional film packaging, such as large mechanical strength, water and oxygen barriers, and good optical properties.

The packaging according to the invention is particularly advantageous for use with stacked units such as individual items, in particular biscuits, cigarette packs or compressed food products.

The perforated film according to the invention facilitates a new kind of packaging solution for cigarette packs. Tobacco packs are laminated and packaged in perforated films according to the invention. Thereafter, these cigarette packs can be opened at predetermined break points by rupturing along the perforation line.

The invention is described in more detail by the following examples:

Example  One

Transparent three-layer ABA films having a symmetrical structure and a total thickness of 20 μm were produced by coextrusion followed by gradual stretching in the longitudinal and transverse directions. The top layer had a thickness of 0.6 μm in each case.

B-base layer:

About 90 wt.%: Propylene homopolymer with melting point of 162 ° C. and melt flow index of 3.4 g / 10 min.

0.15% by weight: N, N-bis-ethoxyalkylamine (antistatic agent)

0.30% by weight: Erucic acid amide

A-upper layer:

About 75 wt%: Statistical Ethylene Propylene Copolymer with C2 Content of 4.5 wt%

About 25 weight%: Statistical ethylene propylene butylene terpolymer with 3 weight% ethylene content and 7 weight% butylene content (the rest propylene)

0.33 wt.%: SiO 2 as an anti-blocking agent having an average particle size of 2 μm

0.90% by weight: polydimethyl siloxane with a viscosity of 30,000 mm 2 / sec

In the individual process steps the production conditions were as follows:

Extrusion: temperature base layer: 260 ° C

           Upper layer: 240 ℃

      Temperature of discharge roller: 20 ℃

Longitudinal elongation: temperature: 110 ℃

Longitudinal stretch ratio: 5.5

Transverse elongation: temperature: 160 ℃

             Lateral elongation ratio: 9

Immobilization: Temperature: 140 ℃

        Convergence: 20%

The film was then coated onto one surface with a sealable acrylate coating.

Thereafter, the film was cut to a width of 350 mm in a narrow section and wound up. These narrow zones (rolls) were fed on a roller with needles in a second working step, thereby providing longitudinal perforations arranged parallel to the film at 6 mm intervals. The perforation had a propeller-yang shape with a length B of 4 mm. The spacing between individual perforations was measured at 2 mm. The perforated film was wound up in a roll of perforated film in this manner.

Then, a film of 12 packs of cigarettes was packaged using a film perforated in this manner. The pack was aligned so that the rim of the pack was aligned with the perforation lines. The pack can be separated by rupturing along the perforation line without propagating any uncontrolled tears in the film.

compare Example

A single row of perforations was made in the film described in Example 1 using the same kind of needle roller. Perforations were the same length as Example 1 and had the same spacing. The film was used in the same way to pack a stack of 12 cigarette packs. The package could not be opened by rupturing. In the case of an attempt to tear the film along the perforation line, the tear propagated out of control in 3 out of 10 attempts to the side of the perforation line.

Claims (11)

A biaxially stretched polypropylene film roll, characterized in that the films run parallel to each other and exhibit at least two perforation lines arranged at a maximum interval of 10 mm, the perforations of the two lines being offset relative to each other. The polypropylene film roll of claim 1 wherein there is a gap of undamaged film between the perforations and the perforations are longer or longer than the gaps between the perforations. The polypropylene film roll of claim 1 wherein said perforation is made using a needle and is circular or elliptical or propeller-shaped. The polypropylene film roll according to claim 1, wherein the perforation is made by a knife and is in a long or rectangular shape. The polypropylene film roll of claim 1 wherein the perforation is a thin spot that represents 10 to 80% of the remaining film thickness. The polypropylene film roll of claim 1 wherein the perforation is 0.1-8 mm long. The polypropylene film roll according to claim 1, wherein the length of the gap between these perforations is 10 to 95% of the length of the perforations. The polypropylene film roll of claim 1 wherein the center of the zone of the first perforation line is in each case aligned with the center of the facing perforation at the second perforation line. Use of the perforated film roll according to any one of claims 1 to 9 for packaging cylindrical or prismatic individual items. Use according to claim 9, characterized in that the individual item is a pack of cigarettes. Cigarette packs produced by the use according to claim 10.

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