GB2414979A - Label treated with adhesive modifying agent - Google Patents

Abstract

There is provided a label which is removable from an article under the action of a hot washing fluid, the label comprising a backing layer which is a polymeric film and a pressure sensitive adhesive layer for bonding the label onto the article, the pressure sensitive adhesive layer having an inner surface which faces towards the backing layer and an outer surface for adhering to the surface of the article, wherein the outer surface of the adhesive layer, prior to its application to an article, is provided with a coating of an adhesive modifying agent. There is also provided a method of manufacturing the same label. The adhesive modifying agent may reduce the adhesive strength of the adhesive layer in the regions to which it is applied. The adhesive modifying agent may be a UV-cured adhesive deadening varnish.

Description

24 1 4979

A LABEL FOR AN ARTICLE

Field of the Invention

The invention relates to a label for an article, in particular for a reusable container, the backing material layer of the label being bondable onto the article by means of an adhesive layer and the label being removable from the article under the effect of hot washing fluid. The articles may be beverage bottles or medicine bottles of glass or plastic, test tubes, repeatedly reusable outer packagings for a multiplicity of individual containers, in particular beverage bottle crates, etc The invention also relates to a method of making the label, an article to which the label has been applied and a method of removing the label from an article to which it has been applied by the application of a hot washing fluid.

Background of the Invention

For example, in the beverage industry, the containers used, for example bottles, are subject to a high quota of reuse. The containers are cleaned with each return before refilling, the labels also being detached during washing of the vessels. Then the vessels are refilled and relabelled corresponding to the beverage type filled. If the vessels are standardised for a particular product group, such as a beer bottle, the bottles returning to the brewery do not need to be resorted according to beer types, as would be the case with permanently pre-decorated bottles. The different labelling usually only occurs after filling. In the case of a direct printing of the bottle which cannot be washed off, large warehouse stocks of the appropriate pre-decorated bottles In the beverage industry, the washing of the vessels, i.e. the bottles, is generally carried out with a hot washing liquid, such as dilute caustic soda, heated to 60 to ALEC., without additional mechanical support In the form of brushes etc. Often, paper labels with wet-glue adhesive are used for the labelling of reusable containers In this case, the wet-glue adhesive is applied to the full surface or in strips, the adhesive only being applied to the paper immediately before labelling. The disadvantage of this label type is that the filler must work with wet glue and the handling of these labels is often more difficult than that of pressure sensitive labels.

Pressure sensitive labels, are obtained from the label suppliers already provided with adhesive.

Because of the standardised washing-off conditions in the beverage industry, it has previously only been possible to use paper-based labels. During washing off of the labels in the wash station, the water permeability and swelling nature of paper is exploited with the object that the adhesive comes relatively quickly into full-surface contact with the washing liquid, and is completely detached in the predetermined washing time-of the order of some minutes. In the case of wet glue applied labels, the adhesives are usually formulated to go into solution in the washing liquid. In the case of pre-coated pressure sensitive labels, redispersible adhesives are often used and the objective is that the adhesive is removed intact with the paper face to avoid contamination of the washing bath. This high permeability for washing liquid and water is not possessed by the thermoplastic films used for many labels, such as polyolefins, polyesters, polyvinyl chlorides, polystyrenes, etc. Such films prevent the access of the washing liquid to the interface of the adhesive and container surface, so that the impermeable film labels can only be slowly detached from the label edge, which, without additional mechanical support, such as brushes, high-press nozzles, etc., does not permit complete removal of the labels within an economically justifiable time span.

These mechanical means are undesirable because of the higher outlay.

In the beverage industry, however, there is an Increasing demand for filmbased labels precoated with adhesive. Such film labels, in contrast to paper labels, can be decorated in an extremely wide range of ways. In contrast to paper, they are also available in transparent form, have excellent wet strength and can be dispensed onto the containers at high speed in standardsed machines, without the need to work with wet adhesives, as is the case of the wet-glue paper label. Their mechanical properties such as tensile strength and extensibility are greatly superior to those of paper labels.

However, it should also be possible to readily wash off such film labels with existing washing systems as easily as the paper labels often used until now.

One solution to the problem outlined above is set forth in US Patent No. 6680097 (Steinbeis), the contents of which are hereby incorporated by reference, which states that a label is detachable from the article with little effort. This is achieved by the use of a label in which the backing material layer comprises a plastic film layer that is stretched In at least one direction and shrinks back under the effect of heat, such as the temperature of the washing fluid or/and by thermal radiation, so as to overcome the retention force of the adhesive layer. By virtue of the effect of the heat, a shrinking back of the plastic film occurs, while at the same time the adhesive loses adhesive force. It is stated that by this means, the label detaches gradually from the article, for example from the edge or with the formation of channels, and can be easily removed within an extremely short time.

Another prior art reference is W002/07474, the contents of which are hereby Incorporated by reference, which discloses a label in which the film is a Copolymer such as cellulose.

US-A-2003/0150148, the contents of which are hereby incorporated by reference, discloses a label which has embossed or debossed portions to correspond to indicia printed on the label.

Summary of the Invention

The present invention provides a label which is removable from an article under the action of a hot washing fluid, the label comprising a backing layer which is a polymeric film and a pressure sensitive adhesive layer for bonding the label onto the article, the pressure sensitive adhesive layer having an inner surface which faces towards the backing layer and an outer surface for adhering to the surface of the article, wherein the outer surface of the adhesive layer, prior to its application to an article, is provided with a coating of an adhesive modifying agent.

According to another aspect of the present invention, there is provided a method of manufacturing a label for attachment to an article, the label being removable from the article under the action of a hot washing fluid, the method comprising applying a pressure sensitive layer to a backing layer which is a polymeric film, and applying a coating of an adhesive modifying agent to the surface of the adhesive layer away from the backing layer.

One example of an adhesive modifying agent is a UV-curedadhesive deadening varnish.

In preferred embodiments in accordance with the present invention, the adhesive modifying agent serves to reduce the adhesive strength of the adhesive layer in the region or regions at which the adhesive modifying agent is applied. However, the expression "adhesive modifying agent" is used in a broad sense to mean any agent which has an effect on the chemical, physical or mechanical properties of the adhesive layer.

The adhesive modifying agent may be applied to the adhesive surface through direct printing by a conventional print process i.e. screen, flexographic, letterpress or gravure.

To effect this, the face material and adhesive part of the construction is first de- laminated from the release liner to allow the printing of the adhesive modifying agent onto the now exposed adhesive face and then re-laminated after printing through a nip roller structure. Such release liners are invariable provided on labels with pressure- sensitve adhesive, to cover the adhesive during transport and handling so as to prevent the adhesive sticking unintentionally to itself or to other articles. The release layer is removed just before the label is affixed to the intended article.

The adhesive modifying agent may be applied to the full surface of the label or In patterns appropriate to the label profile as illustrated in Figure 3.

In a preferred embodiment of the label, the adhesive modifying agent is applied as a series of round dots with the percentage coverage appropriate to the functional requirements of the individual label. Percentages in the range of 5% to 10% have been found preferable. 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.

The purpose of the adhesive modifying agent is to facilitate the lifting of the label edges within the washing bath without any mechanical means other than the turbulence created by the water streams. This then allows the washing solution to penetrate behind the label and effect the washingoff of the label.

The label of the present Invention has been found to exhibit superior wash off characteristics when washed in a hot washing fluid with the adhesives selected. It is presently believed that when an article to which the label is applied is contacted with a hot washing fluid, typically hot water, the hot fluid causes expansion of the polymeric species in the pressure sensitive adhesive and in conjunction with the modifications to the adhesive characteristics at the periphery of the label effecting the lifting of the label at the edges. This allows the hot fluid to gain access behind the label, mobilising components, most particularly surfactants within the adhesive and progressively lifting the label from the article and allowing rapid removal of the label from the article.

Brief Description of the Drawings

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawings in which: figure 1 represents the crosssectional primary composite structure of a typical pressure sensitive label to which no treatment has been made and is typical of the structure using thermoplastic film facestock manufactured for non-returnable 1 5 applications; Figure 2 represents the cross-sectional primary composite structure of the pressure sensitive label herein described, which has passed through the process of printing a modifying agent onto the adhesive surface; and Figure 3 represents the rear aspect of a label of an oval profile described herein demonstrating examples of patterns to which the adhesive modifying agent can be applied to the adhesive surface to achieve the desired effect.

Detailed Description

Adhesive modifying a-tent As previously stated, the outer surface of the adhesive layer, prior to application to an article, includes a printed modification to the adhesive surface.

In one embodiment of the invention, the adhesive modifying agent serves to deaden the adhesive where printed. In other words, the adhesive modifying agent lowers the level of adhesion to the article and allows ingress of washing fluid, such as a caustic solution through the voids between the adhesive layer and the article.

In another embodiment of the invention, the adhesive modifying agent incorporates a component which is soluble in the washing fluid, for example is soluble in a hot caustic solution Thus, the adhesive modifying agent, where printed, lowers the level of adhesion to the article and allows Ingress of caustic through the channels created by the printed pattern which Is readily solubilised in contact with the hot washing fluid In another embodiment of the invention, the adhesive modifying agent incorporates a component which swells when exposed to heat or water and, in particular, swells when exposed to hot washing fluid such as a caustic solution. Thus, the adhesive modifying agent, where printed, swells in the presence of the washing fluid and so lowers the level of adhesion to the article and allows ingress of caustic through the channels created by the printed pattern.

Polymeric film The polymeric film of the label of the present invention may be any suitable polymer film from which labels may be made. For the avoidance of doubt, the polymeric film used in the invention is not a paper. Examples of polymer films are thermoplastic films such as polyolefins, polyesters, polyvinyl chlorides and polystyrenes. Biopolymers such as cellophane or polylactc acid (PLA) may also be used. Particularly preferred are water-impermeable polyolefin films, most preferably polypropylene films, such as baxially-oriented polypropylene (BOPP).

The polymer film may be a laminate or a single layer. It may include additional layers such as metallized layers.

The polymer film is preferably transparent to provide a "no-label" look. It may or may not be coloured to match the colour of an article to which the label is to be attached.

The polymer film may have a thickness typical of films for labels, such as from 15,um to 1 00'um, preferably 40 to 50,um The polymer film may be treated by known methods in the art and may be coated in a manner which is known per se.

Pressure sensitive adhesive The adhesive used in the present Invention is a pressure sensitive adhesive. A characteristic of pressure sensitive adhesives is that they are permanently tacky at the temperature of use, such as room temperature. Pressure sensitive adhesives adhere to a variety of substrates when applied with pressure, do not require activation by water, heat or solvents, and have sufficient cohesive strength to be handled with fingers. The primary bond for a pressure sensitive adhesive is not chemical or mechanical but rather a polar attraction to the substrate, and requires pressure to achieve sufficient "wet-out" onto the surface to provide adhesion. Further information regarding pressure sensitive adhesives can be found in the textbook Pressure- Sensitive Adhesives Technology by Istvan Benedek, Luc J. Heymans, Istran Benedek (Marcel Dekker 1997) Whilst pressure sensitive adhesives are known for use with thermoplastic labels for a "no-label" look, such adhesives are water resistant and, if applied conventionally, are not removable under a hot water wash.

The present invention permits the use of a wide variety of pressure sensitive adhesives, including those which are water resistant. The modification to the adhesive layer permits hot wash water to penetrate and detackify the adhesive so that it is removed from the article complete with the remainder of the label.

In order that the label of the present invention is not removable under the action of cold water, such as water which condenses on the article in a refrigerator or other cold environment, the pressure sensitive adhesive used should be one which is not readily soluble in water.

Examples of pressure sensitive adhesives which may be used in the present invention are ones that do not dissolve in water, at least until detachment of the label, in particular a redispersible adhesive such as a dispersion adhesive based on acrylate or copolymeric acrylate/polyurethane compounds and copolymers with an acrylate proportion (e g. rubber/acrylate).

Preferably the adhesive is applied to the label material covering the full surface or In regions with gaps, if appropriate in patterns.

A cover or release layer may be provided over the outer surface of the pressure sensitive adhesive layer as is well known in the art.

The hot washing fluid may be in the form of a liquid, in particular water and contain surfactants and alkaline agents, in particular caustic soda.

Test Results In one embodiment of the invention, samples of UCB Rayoface CPA50 (50,um bi- axially oriented polypropylene) was transfer laminated with 20gsm of a water-borne pressure sensitive adhesive (HB Fuller, SE5279), described as a high tack, high cohesion, permanent adhesive suitable for paper and filmic facestocks, against a 30 micron siliconised transparent polyester liner, as outlined in Figure 1.

In another embodiment of the Invention, samples of UCB Rayophane 645E721 (64.5gsm Regenerated Cellulose Film) was transfer laminated with 20gsm of the same water-borne pressure sensitive adhesive outlined above.

The samples were then printed on a narrow web printing press and through the process of de-laminating the web it was possible to flexographically print onto the adhesive surface with a uv-curing adhesive deadening varnish (reference L301, supplier Paragon Inks) before re-laminating the web through a nip roller assembly. The web was printed with a range of patterns using a round dot printing structure; An allover pattern was applied at percentages of 5%, 10%, 20%, 30% & 40% A 5mm border to the label was applied at percentages of 5%, 10%, 20%, 30% & 40% A 1 Omm border to the label was applied at percentages of 5%, 10%, 20%, 30% & 40% The varnish was applied using an anilox roller of line count 650 and volume 3.5 cc/m2 The printed samples were cut to shape in-lne through the die-cutting unit and hand applied onto returnable glass beer bottles using a wiper blade mechanism to simulate automatic application.

The labelled bottles were then allowed a minimum of 24 hours standing time at ambient conditions (23 C, 50% RH) prior to undertaking the washing tests, to allow the associated cold creep of the adhesive and adhesion to the glass surface to fully develop.

The washing tests were conducted in a stainless steel bath filled with 12 litres of hot washing fluid agitated via an overhead stirrer at 250 rpm, simulating the conditions within the main soak of an industrial washing environment. The bath was maintained at a temperature of 80 C, 2.0% NaOH concentration and with a 0.1% addition of P3 Stabilon Plus, a washing additive supplied commercially by Ecolab.

The labelled bottles were partially filled with ambient temperature water and then immersed into the bath. The time taken for the label to completely detach from the bottle was measured.

The average of the results obtained for the polypropylene labels described above was less than 5.0 minutes.

The average of the results obtained for the regenerated cellulose labels described above was less than 2 minutes.

In both embodiments, the average wash-off time had been reduced by a factor of around 50% as a consequence of the mechanical treatment described herein, compared to labels that had not been treated In this way.

Claims (1)

1 A label which is removable from an article under the action of a hot washing fluid, the label comprising a backing layer which Is a polymeric film and a pressure sensitive adhesive layer for bonding the label onto the article, the pressure sensitive adhesive layer having an inner surface which faces towards the backing layer and an outer surface for adhering to the surface of the article, wherein the outer surface of the adhesive layer, prior to its application to an article, is provided with a coating of an adhesive modifying agent.

2 A label as claimed in claim 1, wherein the adhesive modifying agent serves to reduce the adhesive strength of the adhesive layer in the region or regions at which the adhesive modifying agent is applied.

3 A label as claimed In claim 1 or 2, wherein the adhesive modifying agent Is a UV-cured adhesive deadening varnish.

4 A label as claimed in any one of the preceding claims, wherein the adhesive modifying agent is coated over the full surface of the label.

A label as claimed in any one of claims 1 to 3, wherein the adhesive modifying agent is coated over the label in a predetermined pattern.

6 A label as claimed In any one of the preceding claims, wherein the adhesive modifying agent is applied over at least part of the outer surface of the adhesive layer as an array of dots.

7 A label as claimed in claim 6, wherein the area density of the dots is between 5% and 10%.

8 A label as claimed In claim 6 or 7, wherein the dots are round 9 A label as claimed in claim 6 or 7, wherein the dots are square. 1 1

A label as claimed in claim 5, wherein the adhesive modifying agent is applied over at least part of the outer surface of the adhesive layer as an array of parallel or Intersecting lines 11 A label as claimed in any one of the preceding claims, In which the adhesive modifying agent is applied as a border at an edge region of the outer surface of the adhesive layer.

12 A method of manufacturing a label for attachment to an article, the label being removable from the article under the action of a hot washing fluid, the method comprising applying a pressure sensitive adhesive layer to a backing layer which is a polymeric film, and applying a coating of an adhesive modifying agent to the surface of the adhesive layer away from the backing layer.

13 A method as claimed in claim 12, wherein the adhesive modifying agent is applied to the adhesive surface through direct printing by a conventional print process.

14 A method as claimed in claim 13, wherein the print process comprises flexographic printing.

A method as claimed In any one of the preceding claims, wherein after applying the adhesive layer to the backing layer: (a) a release liner is applied to the surface of the adhesive layer away from the backing layer; (b) the release liner is delaminated from the adhesive layer, (c) the adhesive modifying agent is applied to the adhesive layer, and (d) the release linems reapplied to the adhesive layer 16 A label substantially as described herein, with reference to and as shown In Figures 2 and 3 of the accompanying drawings.