A label for removable attachment to an article

[0001] The present invention relates to labels affixed to articles in a manner that allows them to be removed. In particular, but not exclusively, the invention relates to labels for attachment to articles in the form of containers, such as glass bottles.

[0002] Traditionally, beverage bottle labels are made of paper and attached to bottles by wet gluing. Labels are delivered without adhesive in this process; glue is applied to the label shortly before applying the label to the bottle. The labeling process usually occurs on the bottling line after the bottle has been filled and closed.

[0003] Recently, labels made of thermoplastic film have become popular. These labels are usually supplied with self-adhesive glue already applied to one surface of the base material, the adhesive layer being covered with a barrier layer that prevents premature sticking. Labels made of thermoplastic film allow for a greater range of decorative effects. Since thermoplastic films can be transparent, the label backing material may be almost invisible, so that the printed material on the label appears to be printed directly on the bottle. In addition, the use of pressure sensitive adhesive avoids the problems that may arise when handling liquid adhesive near a bottling line.

[0004] Typically, bottles are adapted for return and reuse. If the bottles are reused, they may be filled with a drink other than the one they were previously filled and, as a consequence, all labels must be removed from the returned bottles. Label removal installations were developed for paper labels with liquid adhesive. Generally, such installations use bottle washing in hot caustic soda solution. The caustic solution penetrates the paper material of the label and interacts with the adhesive, for example dissolving it, causing the label to separate from the bottle. To assist label removal, mechanical means such as brushes or spraying can be used, or bottles can simply be moved in a caustic solution.

[0005] For economic reasons, there is resistance to major changes on bottling lines. Consequently, bottling companies are reluctant to invest in completely new bottle washing installations that would be adapted to different types of labels. This results in pressure on label suppliers to develop thermoplastic film labels that can be properly removed using conventional hot caustic solutions. The problem that arises in this case is that the hot caustic solution does not significantly penetrate the thermoplastic film, which means that the solution can initially only contact the adhesive at the edges of the label. As a result, the label removal process may be unacceptably slow.

[0006] Various measures have been proposed to accelerate the removal of labels based on thermoplastic film materials. For example, our British Patent Application No. 0419398.3 discloses the use of a heat-sensitive pressure sensitive adhesive that loses peel strength when heated to temperatures found in hot caustic washing installations. The same document also discloses the use of micro-tubules on the transition surface between the adhesive and the bottle to assist the penetration of the washing liquid into the adhesive. These micro-tubules can be made either by embossing the label or by applying an adhesive neutralizing material to part of the adhesive surface.

[0007] US 6680097 discloses a label made of a stretch film that shrinks when heated. The intention of this solution is that the shrinking effect causes the label to pull off along the bottle, thereby degrading the adhesion between the label and the bottle.

[0008] A problem with shrink-based solutions such as disclosed in US 6680097 is that stretched thermoplastic films shrink into a rigid "shell-like" structure that can be difficult to remove from the washing machine and then be trapped. in the working parts of the washing equipment.

In addition, film materials that have adequate shrinking properties at temperatures found in commercial washers are usually either expensive or undesirable in environmental terms.

[0009] According to the present invention, there is provided a label that is removable from a product after heating, the label having a backing layer, which is a polymer film, and an adhesive layer for bonding the label to the product, characterized in that the backing layer is a multilayer structure consisting of polypropylene film and polyester film, where the material of these films is such that the backing layer expands under the action of heat, wherein the degree of expansion of the polypropylene film and polyester film is different such that the label tends to curl into an curvilinear form with an adhesive layer on the outside of the curvature.

[0010] In such a label, when attached to a product, such as a beverage bottle, and placed in a hot caustic bath, forces will be generated, in a spring-like manner, causing certain areas of the label to move away from the bottle. This in turn will allow the washing liquid to penetrate the offset label areas, thereby accelerating the removal process.

[0011] The backing layer comprises a laminate of two different materials having different thermal expansion coefficients. Thus, the material adjacent the adhesive layer will have a higher coefficient of thermal expansion than the latter backing material, so that the label will tend to unwind from the product to which it is attached when heated.

[0012] According to the invention, the two laminate materials forming the backing layer are polypropylene film and polyester film. One or both of these films can be oriented, and preferably biaxially oriented, by stretching. In a preferred embodiment of the label, in which the backing layer consists of a polypropylene / polyester laminate, the polypropylene film is adjacent to the adhesive layer.

[0013] The films of this laminate can be of different thicknesses. For example, one layer may have a thickness of 20% to 75% of the thickness of the other layer. The thicker layer may have a thickness in the range from 15 to 60 pm.

[0014] In the backing layer comprising a laminate of polypropylene and polyester films, the polypropylene film may have a thickness in the range of 15 to 60 μη, more preferably 50 μη, and the polyester film may have a thickness in the range 12 to 30 pm, preferably 19 or

3 pm.

[0015] Biaxially oriented films have a "machine direction" which is the direction in which the film moves during the manufacturing process, and "transverse direction" which is a direction in the film plane extending perpendicular to the machine direction. The properties of the film are usually not the same in both directions. For good results (i.e. optimal curl) in a label according to the present invention having a backing layer comprising a polypropylene and polyester laminate, it is believed that the modulus of elasticity of the polypropylene film is important. It is currently believed that the modulus of elasticity of the polypropylene film in the machine direction is preferably 2000 to 2500 N / mm², more preferably 2100 to 2300 N / mm²and in transverse direction is preferably 3000 to 4000 N / mm², more preferably 3250 to 3750 N / mm². It is currently believed that polyester film having a modulus of elasticity in the machine direction of 4000 to 5000 N / mm provides good results², preferably 4500 N / mm², and 4,500 to 5,500 N / mm², preferably 5000 N / mm².

[0016] In order to better understand the present invention and to show more clearly how it is being implemented, reference is made, by way of example, to the accompanying drawings in which:

Figure 1 shows, in schematic form, the structure of a bottle label;

Figure 2 shows a bottle provided with the label of Figure 1 during the label removal process;

Figures 3a, 3b and 3c show different degrees of rolling of the label; and

Figures 4a, 4b and 4c show the application of the label to the bottle.

[0017] Referring to Figure 1, the label is schematically shown, for readability, enlarged. Generally speaking, the label comprises a backing layer 2 provided on one side with a print layer 4 and on the opposite side an adhesive layer 6. The adhesive layer 6 is provided with a barrier layer 10. Optionally, the adhesive layer 6 has an applied layer 8 neutralizing glue.

[0018] Print 4 is shown as a continuous layer, although in practice only parts of the layer can be printed. Similarly, the adhesive neutralizing layer 8 is applied only to certain parts of the adhesive layer 6, for example as a dot pattern, as described in more detail in our Patent Application 0419398.3, which we cite here.

[0019] The backing layer 2 has a laminate structure and comprises an outer film layer 12 and an inner film layer 14 joined together by laminating technique using laminating adhesive 16. Films 12 and 14 can be of any two materials with different thermal expansion coefficients. Preferably, the outer film 12 has a lower coefficient of thermal expansion than the inner layer 14, so that when heated, the label will roll outwards from the adhesive layer 6.

In other words, the label will roll around the axis above Figure 1.

In a specific embodiment of the label, as shown in Figure 1, the outer layer 12 of the laminate 2 is a biaxially oriented polyester, and is preferably a polyethylene terephthalate (PET) film.

A suitable foil is available under the designation Melinex ® 313. PET has a linear coefficient of thermal expansion in the range of 20 to 80 x 10^-6 K^-1.

[0021] The lower film 14 of the laminate 2 is a polypropylene film and can be a film available from ExxonMobil under the designation Label-Lyte 50LL536. Polypropylene has a linear coefficient of thermal expansion in the range of 100 to 180 x 10^-6 K^-1. It can therefore be seen that the coefficient of thermal expansion of polypropylene is approximately at least twice as high as PET and can be five or more times greater.

[0022] Preferably, the adhesive layer 6 comprises a heat sensitive pressure sensitive adhesive. In the context of the present invention, the term "heat-sensitive" means that the adhesive properties of the adhesive layer are degraded or reduced when heated to a temperature in the range of 40 ° C to 120 ° C, in the presence or absence of washing liquid. Preferably, the reduction in adhesive properties occurs at temperatures in the range of 40 ° C to 90 ° C, and more preferably at temperatures in the range of 50 ° C to 85 ° C. In preferred embodiments, the adhesive properties of the adhesive layer decrease at a temperature in the range of 60 ° C to 80 ° C, and more preferably 65 ° C to 75 ° C.

[0023] The expression "heat-sensitive" is not to be considered as indicating that the adhesive properties of the adhesive layer are temporarily reduced by exposure to a sufficiently high temperature, but over a period of time consistent with the requirements of the washing process. Thus, the reduction in adhesive properties occurs preferably no more than 3 minutes after subjecting the labeled product to the appropriate temperature. However, it is assessed that longer periods of time, e.g., greater than 10, 9 or 5 minutes after subjecting the product to elevated temperature, may still be considered to fall within the broad scope of the present invention.

[0024] The adhesive property that decreases after subjecting the product to elevated temperature is the adhesion or peel strength of the adhesive layer. Preferably, the peel strength is reduced by at least 30%, and in some cases by at least 40% or even 50% after subjecting the product to elevated temperature. In especially preferred embodiments, the peel strength is reduced to about 20% of the peel strength at ambient conditions, i.e. a reduction of 80%. In general, a reduction in peel strength will be sufficient for the purposes of the present invention if the remaining peel strength of the adhesive layer is unsuitable for retaining the label on the product after the product has been subjected to a high temperature mechanical wash liquid during a normal commercial washing process. The industry-recognized peel strength test is described in FINAT Technical Handbook Edition 6 and is FTM1, Peel Strength (180 °) at 300 mm per minute. The peel test describes the durability of adhesion or the discoverability of self-adhesive adhesives. Test strips 25 mm wide are prepared, it is adhered to a test plate (glass or metal) and then checked after a specified time (usually 20 minutes and 24 hours). The force needed to detach the label material from the test plate is recorded in Newtons and the observations regarding adhesive transfer are recorded. For the purposes of the present invention, what is most important is that the peel strength at washing conditions is low, e.g. not more than 5N / 25 mm. The peel strength at ambient conditions depends on the heat sensitivity of the adhesive as well as the weight of the coating, but could be as high as 25N / 25 mm.

[0025] The peel strength that is considered in the context of the present invention is the peel strength of the adhesive layer when the label is applied to the intended product, which may be, for example, made of glass, plastic, metal or ceramic material .

[0026] The pressure-sensitive adhesive may be a permanent solvent-based, water-based or hot-melt pressure-sensitive adhesive, comprising a combination of a polymer component and a surfactant component that allows the label to be removed from the product to which the label is attached, preferably over a period of 10 minutes with an aqueous cleaning agent. temperature between 60 ° C and 90 ° C. The adhesive material may be based on rubber, acrylic or modified acrylic. In a preferred embodiment, acrylic-based adhesives are used, modified to intensify their heat sensitivity so that they meet the abovementioned requirements. Modification of the adhesive base material may include the addition of a surfactant, which may be anionic, amphoteric, cationic, nonionic or polymeric surfactant. When used, the surfactant may contain any one of a variety of organic sulfates, sulfonates, sulfonic acids, salts and mixtures thereof, or sulfosuccinates. When used, the non-ionic surfactant may contain ethoxylated substances, ethoxylated alcohol or alkoxylated alcohol. Preferably, the surfactant is present in the adhesive material in an amount of not more than 5%, preferably not more than 3%, and more preferably not more than 2%. The surfactant is preferably active so that it attaches to functional groups in the adhesive polymer. This avoids the possibility of the adhesive layer being flushed out by the surfactant, e.g. if the article with the label applied is immersed in water below the temperature at which the adhesive layer loses its stickiness. For example, if the product is a beer or wine bottle, it may be immersed in ice water to cool its contents before consumption.

[0027] Preferably, the adhesive material is not resinous, that is, in other words, it loses additional binder or other added resin.

[0028] In achieving the functionality of the label as described herein, it is preferred that the pressure sensitive adhesive be applied to the film material on labels having a basis weight between 10 gsm and 20 gsm. In a preferred embodiment, the thickness of the adhesive layer may be smaller than is conventionally used for label adhesive layers. Preferably, the thickness of the adhesive layer is not more than 15 g / m2² and may not be greater than 14 g / m2²although you can imagine that in most applications the adhesive layer will have a thickness of not less than 10 g / m2².

[0029] Optionally and as shown in Figure 1, the outer surface of the adhesive layer, before being applied to the product, is provided with an adhesive modifying agent coating to provide the adhesive neutralizing layer 8. One example of an adhesive modifying agent is ultraviolet-curing adhesive-neutralizing varnish. [0030] In preferred embodiments using an adhesive modifying agent, the adhesive modifying agent serves to reduce the strength of the adhesive adhesive layer in the area or areas where the adhesive modifying agent is used. However, the expression "adhesive modifying agent" is used in a broad sense to mean any agent that affects the chemical, physical or mechanical properties of the adhesive layer.

[0031] The adhesive modifying agent may be applied to the adhesive surface by a direct printing technique during a conventional printing process, i.e. by screen, flexographic, letterpress or gravure printing. To accomplish this, the face material and adhesive part of the structure is first detached from the barrier liner to allow the adhesive modifying agent to be printed on the now exposed adhesive surface, and then re-laminated after printing with a roller press structure. Such barrier liners are invariably found on labels with self-adhesive glue, covering the glue during transport and handling so as to prevent the glue from unintentionally sticking to itself or to other products. The barrier layer is removed just before the label is attached to the intended product.

[0032] The adhesive modifying agent may be applied to the entire surface of the label or in the form of patterns suited to the profile of the label.

[0033] The adhesive modifying agent may be applied as a series of round dots with a percentage coverage appropriate to the functional requirements of a single label.

[0034] Preferred percentage coverage has been found to be in the range of 3% to 10%, these percentage coverage being based on the material from which the printing rollers are made. The printing structure may also take the form of square dots, parallel or intersecting lines and other structures known to those skilled in the art.

[0035] The mechanism by which the preferred adhesive allows leaching is that when the label is heated to a temperature above 50 ° C, more preferably above 70 ° C, with which the labeled container typically encounters during washing, the label loses stickiness (i.e. tear strength) into the container by up to 50%, i.e. it can be detached faster from the product, although the adhesive, however, retains some stickiness. The decrease in tack occurs quite quickly, preferably within 1 minute of immersion at an elevated temperature. This decrease in adhesive allows the label edge to move away from the container as a result of label curling, as a result of the upward force of label rewinding being greater than adhesion, allowing flushing to be carried out without any mechanical means other than turbulence generated by the jets of water into which it enters the edges of the label as they move from the surface of the product. Furthermore, as these edges stand out from the container, due to the rolling action of the label, the washing solution is able to flow behind the label, between the adhesive layer and the product, and ultimately cause the label to be completely removed by a combination of physical and chemical means.

[0036]

The physical removal of the label is carried out by means of turbulence generated in the washer as a result of its movement, and more specifically by means of pumps generating a strong liquid stream in those places of the machine where the label is removed. The force of the water flow, greater than the adhesive strength of the container, pulls the label from the container.

[0037] Chemical removal of the label is accomplished by contacting the adhesive with a hot cleaning fluid, allowing interaction between the cleaning solution and additives in the adhesive, such as surfactants, which results in eliminating adhesion, thereby preventing the label from re-adhering to the surface of the container or to

NaOH, and soluble or so that they are otherwise as other parts in the assembly of machines.

[0038] Thus, it can be seen that the fundamental property of the adhesive material is its heat sensitivity. This is a significant difference compared to the known pressure sensitive adhesives used on product labels, such as bottles, to be removed in the washing process. Known adhesives have been developed on the basis that conventional washing processes use an alkaline cleaning fluid, such as an aqueous solution, and therefore made ineffective in the presence of such an alkaline fluid. Known adhesives are not sensitive to heat and consequently their properties are not influenced or only slightly affected by heat alone (e.g. by immersion in hot water).

[0039] To attach the label shown in Figure 1 to the bottle, the barrier layer 10 is removed, exposing the adhesive 6 with its adhesive neutralizing layer 8, which is then applied to the bottle under pressure, for example, rollers.

[0040] In its unstressed state at normal ambient temperatures, the label shown in Figure 1 is generally flat. Thus, when applied to a bottle having a cylindrical shape, the label is curved around the bottle and acts as a strained spring, attempting to regain its flat configuration and thus trying to overcome the adhesive effect and regain its flat configuration. Under normal conditions of use of the bottle, the adhesive strength of adhesive 6 is sufficient to maintain the label in full surface contact with the bottle.

[0041] However, when immersed in a hot washing liquid, such as dissolved caustic soda, heated to a temperature between 60 ° C and 90 ° C, for example 60 ° C, the peeling strength of the adhesive sensitive to heat. In addition, the tensioned label is not only forced to adopt its flat configuration, but, as a result of the heat coming from the washing solution, various degrees of expansion of PET and polypropylene film 12 and 14 cause the label to unwind from the bottle, as shown in Figure 2. Initially, when the label is essentially in total surface contact with the bottle, the unwinding effect is compensated by adhesive 6, but nevertheless the force causing the edge to stand out from the bottle increases significantly, which accelerates the penetration of the cleaning solution between the label and the bottle. After all, the label essentially completely unwinds from the bottle and either comes off automatically or as a result of mechanical brushes, showers or mixing in the cleaning solution.

[0042] To assess the effectiveness of a label according to the present invention, it is possible to measure the extent of unwinding of a label with specific dimensions (50 mm x 70 mm) under the action of heat when it is not attached to the product. Therefore, the labels were tested by immersion in a 1-liter beaker containing the washing solution at various temperatures. Preferred labels according to the present invention show unwinding over 180 ° at a temperature below 60 ° C. An example is shown in Figures 3a, 3b and 3c, showing the curvature of the label at different temperatures marked. According to the above procedure, specific examples of label materials according to the present invention were tested at temperatures of 80 ° C, but containing laminates of biaxially oriented polypropylene and PET film of different thicknesses, and the resulting unwinding distance was measured. The results obtained are shown in the Table below:

TABLE

<td>Film thickness polypropylene μπι (A)</td><td>PET film thickness μπι (B)</td><td>Angle collapse</td><td>B / A%</td>

<td> 50</td><td> 23</td><td> 360°</td><td> 0,46%</td>

<td> 35</td><td> 23</td><td> 360°</td><td> 0,66%</td>

<td> 50</td><td> 19</td><td> 405°</td><td> 0,38%</td>

<td> 35</td><td> 19</td><td> 420°</td><td> 0,54%</td>

<td> 50</td><td> 15</td><td> 405°</td><td> 0,30%</td>

<td> 35</td><td> 15</td><td> 420°</td><td> 0,43%</td>

<td> 50</td><td> 12</td><td> 360°</td><td> 0,24%</td>

<td> 35</td><td> 12</td><td> 420°</td><td> 0,34%</td>

As mentioned above, both PET film 12 and polypropylene film 14 are biaxially oriented. The properties of biaxially oriented films are different in the machine direction and transverse to the machine film. In practice, it has been found that after joining with the lamination technique as shown in the Figure

1, the axis around which the coiling occurs varies depending on the method of producing the film 14.

[0044] Oriented polypropylene films can be made by blown film or by stretching. In the blown film technique, the polymer passes through an extrusion head that forms a sleeve out of it, which is inflated between the extrusion head and a pair of nip rollers. The bladder stretches the film in the transverse direction, while the nip rollers stretch the bladder in the machine direction by pulling the film at a rate greater than the speed of its exit from the extrusion head.

[0045] In the stretching process, the polymer is extruded through a flat die in the form of a sheet. This sheet passes through rollers that move at speeds that stretch the machine film, while orientation in the transverse direction to the machine film is obtained by means of a stretching machine in which the film is gripped by its edges and stretched. [0046] It has been found that, if no special measures are taken, oriented polypropylene films produced by the film blowing technique tend to curl in the transverse direction, i.e. the curl occurs around an axis which runs parallel to the machine direction of the film so that the label tends to to curl into a cylinder that extends in a different direction in the machine direction.

It is normal practice for labels delivered in rolls to be applied to bottles so that the machine direction of the label extends around the bottle as shown in Figure 4a. This is because the web runs parallel to the direction of movement of the bottles when the labels are applied. However, if a label with this property is applied to a cylindrical article, such as a bottle, it will then be curved around the bottle so that the machine direction of the film is curved. This is shown in Figure 4b. Thus, the resulting curved label resists any tendency to curl about an axis parallel to the plane in which the curved machine direction of the film lies. In other words, the label will resist unwinding from the bottle at its upper and lower edges and it is possible that this resistance will overcome any tendency to curl in response to different expansion of the label layers. Consequently, it would be desirable for the label to tend to curl about an axis perpendicular to the machine direction such that the label unwinds from a cylindrical article about an axis that is parallel to the longitudinal axis of the article, as shown in Figure 4c.

[0047] By adopting special measures, for example selecting appropriate grades of oriented polypropylene films (for example those known to be suitable for use in the production of labels) and using a stretching process, it was found that it is possible to produce labels that tend to curling around an axis parallel to the machine transverse direction. Therefore, such labels tend to unwind from a bottle or other curved container by unwinding from the bottle at its side edges.

Spear Group Holdings Limited Representative:

78P26583PL00

EP 1 866 895 B1