WO2004031049A1

WO2004031049A1 - Wrapping method

Info

Publication number: WO2004031049A1
Application number: PCT/US2003/030816
Authority: WO
Inventors: Andreas Mayer
Original assignee: Dow Global Technologies Inc.
Priority date: 2002-10-02
Filing date: 2003-09-30
Publication date: 2004-04-15
Also published as: AU2003277101A1

Abstract

The invention provides a method for wrapping a load with at least one thermoplastic film comprising a cling outer surface and a non-cling outer surface, said method comprising at least one wrapping cycle essentially consisting of steps A and B. In step A, the film is wrapped around the load such that its non-cling surface faces towards the inside, that is the load, and its cling surface faces towards the outside, that is the exterior. In subsequent step B, the same or a different thermoplastic film is wrapped around the load such that its cling surface faces towards the load and is in contact with and capable of adhering to the cling surface of the wrap produced in step A. The invention is also concerned with the wrapped load produced by said method and an apparatus suitable to perform said method.

Description

WRAPPING METHOD

The present invention relates to a method suitable for packaging and surface protection. In particular, the invention provides a method for wrapping a thermoplastic film around a load. The invention is also concerned with the wrapped load produced by said method and an apparatus suitable to perform said method. Furthermore, the invention provides new thermoplastic one-sided cling film.

Shrink wrapping and stretch wrapping are used in bundling applications where it is desirable to securely hold and/or package an article or a plurality of articles, for example, for transportation and storage. Applications of particular interest include, for example, the bundling of foodstuff and non-food items as well as goods which are supported on a pallet. The containment and unitizing of pallet loads is a commercially important bundling operation. Load palletization may be accomplished manually or by various automated methods including the methods and apparatus described in U.S. Patents Nos. 5,054,263; 5,020,300; 4,779,396 and 4,754,594.

Shrink wrapping, for example, shrink palletizing, typically comprises overwrapping a load with a pre-formed bag or sheet made from heat-shrinkable thermoplastic film and shrinking the film around the load by applying sufficient heat, for example, using a shrink tunnel, to provide a unitary, tight package. Such use of heat-shrinkable film is described, for example, in U.S. Patent Nos. 3,793,798 and 3,626, 654. Stretch wrapping involves the production of a unitary package by tightly stretching a thermoplastic film around a load and self-sealing of the stretched film without the application of heat. Typically, films exhibiting cling properties on one or both surfaces are used to prevent the undesired unraveling from the load. For example, films for use in stretch wrapping are disclosed in EP-A- 287 272, WO-A- 95/ 15851, WO-A- 96/29203, EP-A-1 022 131 and US-A- 2002/0050124. State of the art cling film structures include multilayer films comprising a cling outer layer, a non- cling outer layer and one or more intermediate layers. In conventional wrapping operations employing such films, the load is enveloped in a multilayer wrap, with the cling surfaces of the layers forming the wrap facing towards the interior, that is the load, and the non-cling surfaces, for example, the slip surfaces facing towards the exterior, that is the environment, for example, the neighboring package. In such wrapping structure, the cling performance between the individual film layers is substantially determined by the interaction of the cling surface with the non-cling surface, for example, the slip surface. The slip behavior between two neighboring packages is determined by the interaction of the slip surfaces on the outside of each package. Machines which are designed to wrap a load with a stretched film to cover and contain the load with stretched layers of film are generally known as stretch wrapping machines. Such machines are known in the art.

The state of the art wrapping technology has some known drawbacks and limitations. One of the problems of both shrink and stretch wrapping methods is that the primary strength and reliability of the package is determined by the consistent quality of the seal. A disadvantage of current wrapping methods utilizing film exhibiting cling surface functionality on one side and non-cling surface functionality on the other side is that these functionalities must be balanced against each other, leading to non-optimal cling and non- cling, for example, slip, performances, respectively. Cling films exhibiting substantial cling properties on both the exterior surface and the inner surface have the disadvantage of retaining dirt and dust and undesirably adhere to adjacent goods or similarly wrapped packages when abutted against one another. Adhesion to adjacent goods or packages typically causes ripping, tearing, distortion and/or unraveling of the film during subsequent handling. There is the need for improved wrapping technology, including a new and improved wrapping method, apparatus and film, which avoids or alleviates the shortcomings of the state of the art technology.

It is an object of the present invention to meet these and other needs. A particular object of the present invention is to provide wrapping technology enabling the substantially independent design of the cling surface functionality and the non-cling surface functionality of a thermoplastic film.

In one embodiment, the present invention provides a method for wrapping a load with at least one thermoplastic film comprising a cling outer surface and a non-cling outer surface, said method comprising at least one wrapping cycle essentially consisting of steps A and B. In step A, the film is wrapped around the load such that its non-cling surface faces towards the inside, that is the load, and its cling surface faces towards the outside, that is the exterior. In subsequent step B, the same or a different thermoplastic film is wrapped around the load such that its cling surface faces towards the load and is in contact with and capable of adhering to the cling surface of the wrap produced in step A. In another embodiment, the present invention provides a method for the surface protection of a load comprising partially or completely covering the surface of said load with at least two layers of one or more one one-sided cling films using the wrapping method provided herein.

In another embodiment, the present invention provides a wrapped load which is at least partially enveloped by at least two layers or wraps of thermoplastic film comprising a cling outer surface and a non-cling outer surface. The multilayer wrap around the load is characterized in that the non-cling surface of the innermost layer of said wrap faces towards the load, the cling surfaces of two adjacent wrap layers are in contact with and adhere (cling) to each other and the most outer surface of the wrap is formed by a non-cling surface.

In yet another aspect, the present invention relates to an apparatus for wrapping a thermoplastic film around a load which apparatus is suitable for carrying out the method of the invention.

Yet another aspect of the present invention relates to a new thermoplastic one-sided cling film.

Definitions

As used herein, the following terms have the specified meanings.

The singular generally includes the plural, and the plural generally includes the singular unless indicated otherwise.

The term "comprising" as used herein means "including".

The term "copolymer" as employed herein means a polymer wherein at least two different monomers are polymerized to form the copolymer. The definition includes terpolymers. The term "interpolymer" is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes, for example, copolymers, terpolymers.

The term "film" as used herein refers to a flat article and includes a sheet, a strip, a tape, and a ribbon.

The term "a load" refers to one article, a plurality of the same or different articles, or assemblages of individually packaged items. The load may include a suitable support, such as a pallet, a tray or the like.

A one-sided cling film is defined as a thermoplastic mono- or multilayer film exhibiting significant cling properties on one outer surface and reduced or essentially no cling on the other outer surface. Said definition includes so-called differential cling film. Generally preferred for the use in the present invention is a thermoplastic mono- or multilayer film exhibiting significant cling properties on one outer surface and essentially no cling on the other outer surface. All parts and percentages are by weight, unless indicated otherwise.

Unless otherwise stated, any given range includes both endpoints used to state the range.

The present invention provides an improved method for wrapping the circumference of a load with a thermoplastic one-sided cling film, in which wrap the cling surface of said thermoplastic film is in contact with and substantially adheres to the cling surface of the same or another thermoplastic one-sided cling film. The cling performance within the wrapping is substantially determined by the interaction of the cling surfaces. The method of the present invention offers the benefit that the two different surface functionalities of the film or films, that is the cling functionality and the non-cling functionality, may be designed and optimized independently from each other. The method is particularly suitable for shrink wrapping, stretch wrapping, stretch-bundling or tension- winding operations for wrapping or holding small and large items, in particular pallet load wrapping, silage wrapping and paper reel wrapping. The wrapping method of the present invention may involve partial or complete coverage of the load with a one-sided cling film. If desired, two or more, preferably two, different one-sided cling films may be utilized for said method. The method of the invention is suitable for the wrapping of an essentially rectangular load, in particular a pallet. Preferably, such wrapping method of the invention comprises the cross-type layer build-up of a cocoon-like or net-like wrap formed by at least two film layers wound in opposite directions, preferably in a substantially spiral configuration. Furthermore, the method of the invention is suitable for the wrapping of an essentially cylindrical load, in particular a silage bale or a paper reel. Preferably, such wrapping method of the invention comprises the cross-type layer build-up of a cocoon-like or net-like wrap formed by at least two film layers wound in the same direction.

The method of the invention comprises one or more wrapping cycles, each consisting of step A and step B. In step A of the cycle, which precedes step B, a portion of the onesided cling film is wound around the load such that the non-cling surface of the wrapping film faces towards the inside, that is the load, and the cling surface faces towards the outside, that is the exterior. In subsequent step B, another portion of the same or a different thermoplastic one-sided cling film is wound around the load such that its cling surface faces towards and is substantially in contact with the cling surface of the film layer wound around the load in step A and that its non-cling surface faces towards the exterior. The number of wrap layers wound around the load in step A or step B may be one or more, taking into account technical and/or economic requirements. The winding operation of step B may be performed in the opposite direction or in the same direction relative to the winding operation of step A.

The wrapping method may comprise more than one wrapping cycles, for example, two, three or four cycles, with the provisio that the non-cling surface forms the exterior of the package or the wrapped load. The wrapping cycle is performed as often as required to obtain the desired package quality and security, as reflected, for example, in high package strength and good puncture and tear resistance . Advantageously, the number of wrapping cycles and the amount of wrapping material used is minimized, for example, for cost and/or environmental reasons, however, without compromising wrapping quality and/or load security.

As readily understood by the person of ordinary skill in the art, certain particulars of the wrapping method are dependent upon the employed wrapping technology, for example shrink wrapping or stretch wrapping, and the utilized machinery. The features, aspects and advantages of the present invention can readily be integrated into conventional automated wrapping systems, such as spiral wrapping machinery, vertical and rotating load wrapping systems, and ring film wrapping systems. Alternatively, the method of the invention can be integrated in manual hand wrapping systems. A preferred method of the present invention is stretch wrapping, preferably using a spiral wrapping apparatus. Spiral wrapping machinery and the use thereof are known in the art. For example, one such apparatus is disclosed in U.S. Patent No. 3,857,486.

In a preferred embodiment, the method of the invention relies on a spiral wrapping apparatus to apply the thermoplastic one-sided cling film to the load, for example, a pallet load. The film is guided from a dispensing means, for example, a roll, and wound around the load to be wrapped in a spiral configuration. The wrapping cycle may start at any suitable place of the load, for example, at the bottom or at the top (step A), advantageously after taking measures to avoid unraveling of the film, for example, after suitably securing a free end portion of the film, or film tail, to the load. Going upward (or downward), the film — its cling surface facing towards the outside and away from the load - is wound around the load in a manner that there is a defined extent of overlapping, including essentially no overlapping, of the film. Typically, for surface protection applications a significant extent of overlapping is desirable. At the top (or at the bottom), the film is reversed such that the cling surface faces towards the load. Alternatively, a second one-sided cling film may be fed in. When, in step B of the wrapping cycle, winding of the film around the load is performed in the opposite direction (for example, downward or upward), the (second) cling surface is brought into contact with the (first) cling surface facing the exterior (as a result of step A). The first and the second cling surface significantly adhere or cling to each other. In a stretch wrapping method of the present invention, the film is stretched as it is wound around the load, yielding a tight, unitary package. In a shrink wrapping method of the present invention, a heat-shrinkable film, for example, a pre-oriented film, is loosely wound around the load. After completion of the wrapping operation, for example, after formation of a cocoon-like or net-like wrap, the film is severed from the dispenser and a free end portion of the film, or film tail, is secured to the wrapped load. Shrink wrapping further comprises the application of heat, for example, in a shrink tunnel or employing other suitable means, to tightly shrink the wrap around the load. In another preferred embodiment, the above described method of the invention is adjusted to be suitable for silage wrapping or paper reel wrapping. In such embodiment, the method comprises winding the film around the load, preferably in a single wrap, such that the non-cling surface faces towards the load and the cling surface faces towards the exterior (step A). After the load is partially or completely covered with the thermoplastic film, the film is reversed such that its cling surface faces towards the load and capable of adhering to the wrap wound around the load in step A and that its non-cling surface faces towards the exterior. In step B of the wrapping cycle, winding around the load is continued in the same direction relative to the winding operation of step A. A preferred method of the present invention is a stretch wrapping method comprising the steps of: positioning a load in a position to be wrapped; placing the leading end of a thermoplastic one-sided cling film from a roll of stretchable film mounted on a moveable dispensing means adjacent to, or on the load; causing relative movement between said roll of film and said load to wrap said film around said load; optionally stretching said film as it is transported to the load, performing at least one wrapping cycle consisting of step A and step B, as described herein, and clamping or cutting the film such that the rest of the film can be retained for wrapping of another load.

The relative movement may involve rotating the load relative to the film dispenser, for example, by positioning the load on a rotating turntable. As it rotates, the load pulls the film from the roll. The film stretching may be accomplished using methods known in the art, for example, by restricting the film unwind movement, for example, with a braking device which applies a restrictive force on the film roll and subjects the film to a braking force causing it to stretch as it is wrapped around the load. The restrictive force is preferably applied by utilizing a roller assembly to engage the outside of the film roll and apply a constant force on the film roll by uniformly stretching the film as it leaves the roll.

Preferably, the film is stretched during the winding operation, for example from 50 percent to 350 percent. Optionally, the film may be pre-stretched , for example, by passing the film through two rollers, the second of which runs faster than the first, before wrapping the film around the load. Stretching significantly reduces the film cost per load. Alternatively, a pre-oriented film may be used. Such film has been pre-oriented off-line, for example , by the film converter or distributer. In this case, the film is wrapped around the load involving no or little stretching, for example, in the range of from 0 to 50 percent stretching.

The present invention further provides a method for the surface protection of an article, or a group of articles, for example, the temporary protection of surfaces during manufacturing or transportation, comprising covering the surface of an article using a wrapping method provided herein. The method may involve unstretched or stretched film.

The load to be wrapped by the method of the present invention may be composed of foodstuffs, for example, canned or frozen foodstuffs, containers, for example, containers containing liquid, rolls of carpet or fabric, agricultural bales, for example, silage bales, paper reels, and other goods to be containerized and/or palletized for shipping/storage and/or display.

The present invention is also directed at the load wrapped according to a method of the invention. Such wrapped load is characterized in that the wrapping is produced by a method of the invention and optionally, in addition to the article or group of articles, may comprise a suitable support , such as a pallet or a tray.

In a preferred embodiment, the present invention relates to the stretch- wrapped load resulting from a wrapping method of the invention.

The present invention further provides an apparatus for performing the method of the invention, for example, comprising a ring film wrapping system or a spiral wrapping system. More specifically, the present invention further provides an apparatus for wrapping a thermoplastic one-sided cling film around the circumference of a load comprising: a means for dispensing the film to be wrapped around the load; means for rotating the film reel by 180 degrees after performance of step A of the wrapping cylce; means for rotating the load relative to the dispenser means; means for clamping or cutting the film of the wrapped load; and, optionally a wiper.

With such an apparatus, step B of the wrapping cycle is continued with the same film.

In another embodiment, the present invention provides an apparatus for wrapping a thermoplastic one-sided cling film around the circumference of a load comprising: two units for dispensing a film to be wrapped around the load; means for rotating the load relative to the dispenser means; means for clamping or cutting the film of the wrapped load; and, optionally a wiper. After step A of the wrapping method is completed with a first one-sided cling film from the first film dispensing unit, step B is performed by attaching a second one-sided cling film from the second dispensing unit to the load wrapped in step A and continuing with the wrapping process.

The preferred one-sided cling films suitable for use in the present invention have substantial cling properties on one outer surface and substantially no cling properties on the other outer surface. The cling of a given exterior cling surface is such that it is sufficient to obtain a good self-seal between the cling surface and an adjacent surface of itself, for example, when portions of the film are overlapped (cling-cling interaction). Several techniques are known to impart or enhance the cling performance of a film.

The desired cling property may be inherent, or be imparted by a tackifying additive, a functional ethylene polymer, such as an acrylate/acrylic monomer, or a grafted polymer, or any combination thereof. Inherent cling does not rely on the addition of a cling agent, such as a tackifying agent, but is substantially imparted by the polymer forming the cling layer. Polymers offering inherent cling are known to those skilled in the art. For example, factors affecting the inherent cling of an ethylene/alpha-olefin copolymer include comonomer content, density and low molecular weight extractables, such as n-hexane extractables. As the comonomer content of the polymer increases, or the density of the polyethylene forming the cling layer decreases, the cling properties improve. As the content of n-hexane extractables increases, the cling properties improve. A tackifying additive, also referred to as tackifier, is a non-film-forming, migratory substance, typically of low molecular weight, minor amounts of which provide sticky or adhesive qualities to polymers, surfaces, films or articles. Compressor oils and processing stabilizers, such as antioxidants, UV stabilizers, antiblock agents are excluded from this definition. Suitable tackifiers are kown in the art and are advantageously selected such as to be compatible with the film forming polymer. Tackifiers commonly used to impart cling to an olefin film layer include, for example, polybutenes, polyisobutylenes, atactic polypropylenes, aliphatic and aromatic hydrocarbon resins, terpene resins, alkali metal and glycerol stearates, oleates, hydrogenated rosins and rosin esters. Preferably, the cling films or layers used in the present invention are substantially free of (purposely) added tackifier, that is the polymer or polymers employed in the cling layer contains less than 1 percent, preferably less than 0.1 percent, of tackifier.

Preferred cling films for use in the present invention are multilayer structures comprising a cling surface layer and at least one additional non-cling layer which imparts other (that is non-cling) properties, such as slip, anti-block, tear- and puncture resistance, optical stability, thermal stability, or any desired combination of such properties. The term "non-cling" is defined herein as the amount of cling of a given exterior layer which is insufficient to obtain a good self-seal when used in stretch cling operations although the layer may exhibit a small amount of measurable cling.

More preferred cling films are multilayer films comprising a cling surface layer, a non-cling surface layer and optionally one or more additional layers, for example a core layer between the cling layer and the non-cling layer. For an ethylene copolymer, non-cling properties typically increase with decreasing comonomer content or higher density. Polymers imparting non-cling properties include, for example, polyamides, polypropylenes or ethylene/alpha-olefins having a density of more than 0.940 g/cm³.

Most preferred multilayer structures comprise an A/B or A/B/C film structure wherein the A layer is the cling layer and the B layer, or in an A/B/C construction, wherein the B layer is a core or structural layer, the C layer, is the non-cling layer, preferably a layer exhibiting slip properties, anti-blocking properties or both, slip and anti-block properties . The non-cling surface layer contains an anti-blocking and/or slip additive and/or another component or raw material which imparts a capability of self-slip, that is the capability of relative movement between this layer and an adjacent layer of itself. Such embodiment overcomes the problem of the tendency of a pallet load overwrapped with a stretch wrap film possessing cling on both of its major surfaces from destructively pulling away from a similarly overwrapped pallet load with which it is in contact. The slip additive present in the non-cling surface layer may be any of those known to be suitable for this purpose, such as fatty acid erucamides or fatty acid oleamides. The slip agent may be present in an amount effective to impart slip properties, preferably in an amount of from 200 to 1000 ppm. Other additives, for example, anti-blocking additives and coefficient of friction reducing agents may (also) be present in the non-cling surface layer of the multilayer film structures.

Suitable anti-blocking additives include, for example, calcium carbonate, silica and/or talc. Such additives are used in an amount effective to impart the desired anti-blocking properites, for example, in the range of from 1000 to 3000 ppm.

The core layer or structural layer can be varied to meet application specific film strengths requirements .

The multilayer cling film may be made from two or more film layers including A/B and A B/C film structures by any film lamination and/or coextrusion techniques or any blown or cast film extrusion equipment known in the art. The preferred multilayer structure is an A/B/C structure, preferably made by coextrusion techniques, more preferably by cast coextrusion techniques.

One-sided cling films can be prepared by corona discharge treatment of monolayer and multilayer films, However, as indicated in U.S. Patent no. 4,425,268, functional polymers and copolymers may still be required to obtain the desired cling properties.

Preferably, the cling layer is formed from an ethylene copolymer, or blends thereof. The stretch/cling films used for the purpose of the present invention have cling in the stretched state, that is when being about or more than 50 percent stretched. Cling force is reported as the force in grams per centimeter (or grams per inch) required to peel apart two strips of film and determined according to methods known in the art. Factors which affect the cling performance of a cling layer formed from an ethylene/alpha-olefin copolymer include, for example, percentage of comonomer content and type of comonomer, extractables content, for example, n-hexane extractables content, the thickness of the film, the stretch and the force applied on the film, and the load.

The one or more additional layers may be formed from other polymers or substrates, for example, polypropylene, polyester, HDPE, LLDPE, EN A, HP-LDPE, paper, metal foil. For example, according to the present invention cling versus slip characteristics in a single film can be optimized by using a high cling resin, such as a low density ethylene/alpha-olefin copolymer, for example, such copolymer having a density of up to 0.890 g/ccm, or an ethylene vinyl actate (EN A) copolymer in combination with a low coefficient of friction grade, for example, slip/anti-blocking versions of LLDPE, HDPE or a polypropylene. High cling resins are commercially available and include, for example, AFFINITY ™ polyolefin plastomers commercially available from The Dow Chemical Company. Alternatively, a standard cling grade, for example, an ATTANE ™ polymer or an AFFINITY™ grade recommended for use in blown films, as commercially available from The Dow Chemical Company, can be used in combination with any slip grade to improve film handling, for example, decrease unwinding noise.

The present invention provides a pallet wrap film comprising a cling side made from a VLDPE or a LLDPE and a slip side made from HDPE or a polypropylene. Such film has a very low coefficient of friction and high holding force, which increases with the average density of the film. The present invention further provides a film suitable for paper reel wrapping comprising a cling side of VLDPE and a slip side of polypropylene. Such film has improved scratch and abrasion resistance on the outside.

Furthermore, the present invention provides a film for silage wrapping having a cling side formed from a polyolefin plastomer (POP), as available, for example from The Dow Chemical Company, and a slip side formed from a polyamide. Such film offers the benefit of better oxygen barrier due to the outside and improved welding effects even at ambient temperature as a result of cling-cling interaction.

The present invention further provides a film for shrink wrapping comprising a cling layer formed from POP and the rest of the film formed from LDPE. Such film is made by cast extrusion techniques and has a high orientation in the machine direction. The film is particularly suitable for handshrink applications. It is also envisioned that a monolayer plastic film having two different functional surfaces one of which exhibits significant cling is used in the present invention.

Monolayer and multilayer films may be formed by any suitable extrusion or coextrusion technique or combination of techniques. For example, multilayer films may be formed by extrusion coating, blown film extrusion, cast film extrusion, extrusion lamination, or by combining two or more single film layers.

The total thickness of the monolayer or multilayer film may vary widely based on the desired application. Typically, a suitable multilayer film has a thickness in the range of from 5 to 250 microns in the unstretched state. The composition and the thickness of the cling film is selected to meet the equipment capabilities and the end use performance requirements of the film.

Stretch film for use in this invention can, if desired, be provided in the non-stretched, that is unoriented, or at most only modestly stretched state prior to use or it can be provided as pre-stretched film with little, if any, additional stretch being applied to the film at the time of use.

Either or both exterior surfaces of the film used in the present invention may be modified by one or more suitable post-forming operations, such as corona discharge, chemical treatment, flame treatment. Such treatment may be used to impart desirable characteristics to a flim surface or surfaces, for example, to modify the printability or ink receptivity.

The invention is illustrated by the following Examples. However, these Examples may not be construed as limiting the invention in any way.

Example 1 : A cast pallet wrap film is made using ATTANE™ SC 4106, as available from The Dow Chemical Company, to form the cling layer and HDPE DSC 10101, as available from the Dow Chemical Company in the adjacent slip layer. Such film exhibits good cling performance using the wrapping method of the invention relying on cling-cling interaction, but not using the conventional wrapping method relying on cling-slip interaction. The advantage of the wrapped load is a very low coefficient of friction on the load surface. Example 2: Using the conventional wrapping method relying on cling-slip interaction, a blown silage wrap film made from AFFINITY KC 8852 in the cling layer and a medium to high density polyethylene grade, such as DOWLEX™ 2740, as available from The Dow Chemical Company, exhibits sufficient cling performance only on addition of polyisobutylene (PIB). According to the method of the present invention, addition of PIB is not necessary anymore. As another benefit of the PIB free film enabled by the present invention, oxygen barrier properties are improved.

Example 3 : A pre-stretched threelayer film having a thickness of 23 microns and the following composition is made:

Cling side: ATTANE SC 4107 (10 percent)

Core layer: DOWLEX

Slip layer: Polypropylene PP 319 (The Dow Chemical Company) (10 percent). Using standard method ASTM D 5458-95, cling performance is determined to be as follows:

Cling - cling: 75 g

Cling - slip: 0 g

Slip - slip: 0 g. Using standard method ASTM D 1894-01, the coefficient of friction is determined to be as follows:

Cling - cling: not possible to measure

Cling - slip: 1.2 (kinetic) and 3.1 (static)

Slip - slip: 0.547 (kinetic) and 0.682 (static).

Claims

1. A method for wrapping a load with at least one thermoplastic film comprising a cling outer surface and a non-cling outer surface, said method comprising at least one wrapping cycle essentially consisting of steps A and B; wherein step A comprises wrapping the film around the load such that its non-cling surface faces towards the inside, and its cling surface faces towards the outside, and step B comprises wrapping the same or a different thermoplastic film around the load such that its cling surface faces towards the load and is in contact with and capable of adhering to the cling surface of the wrap produced in step A.

2. A method for the surface protection of a load comprising partially or completely covering the surface of said load with at least two layers of one or more thermoplastic films, which film or films comprises a cling outer surface and a non-cling outer surface, which method comprises at least one wrapping cycle essentially consisting of steps A and B; wherein step A comprises wrapping the film around the load such that its non-cling surface faces towards the inside, and its cling surface faces towards the outside, and step B comprises wrapping the same or a different thermoplastic film around the load such that its cling surface faces towards the load and is in contact with and capable of adhering to the cling surface of the wrap produced in step A.

3. A wrapped load which is at least partially enveloped by at least two layers or wraps of a thermoplastic film comprising a cling outer surface and a non-cling outer surface, wherein the wrap is characterized in that the non-cling surface of the innermost layer of said wrap faces towards the load, the cling surfaces of two adjacent wrap layers are in contact with and adhere to each other and the most outer surface of the wrap is formed by a non-cling surface.

4. An apparatus for wrapping a thermoplastic film around a load which apparatus is suitable for carrying out the method of claim 1.

5. Use of a thermoplastic one-sided cling film in the method of claim 1.