DE29712526U1 - Transfer label or peel-off label with protective ink layers and containers with such a peel-off label - Google Patents

Description

Ti. July 1997 *; I.. : : .* : '.Müüir-Bore & Partner

Applicant: Heineken Technical Services B.V.

Brandt Technologies, Inc.

"Transfer label or peel-off label with printing ink protective layers and containers with such a peel-off label"
Our sign: H 2087 - ru / he

Transfer label or peel-off label with protective layers for printing inks and containers with such a peel-off label

Description

The invention relates to a transfer label or a transfer inscription or a peel-off label with a carrier or support layer and a transfer layer which is detachably attached to the support layer, wherein the transfer layer comprises a printing ink layer.

The invention also relates to a container equipped with a transfer layer according to the invention.

It is well known in the packaging arts to label containers such as plastic boxes by applying a non-removable, permanent image to them using a screen printing process. Such labels provide a highly durable finish with availability of two or three colors. However, this technique offers a limited number of colors, does not have the refined graphic designs offered by other labeling methods, is not flexible in its ability to accommodate changes in graphics to suit market strategies, resulting in large inventories of obsolete units, and tends to show signs of wear after approximately four cycles.

When removable inks are applied to recyclable plastic crates by a screen printing or ink pad printing process

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the printing inks must be applied in the bottling plant, such as a brewery, which can lead to problems with regard to approval. After removal from the crates using a crate washing device, the printing inks will dissolve in the washing liquid and thus contaminate the crate washers. Furthermore, the speed of application is limited and the curing of the printing inks requires a lot of space and long storage times before delivery.

A second way of labeling containers involves sticking printed paper labels onto containers such as plastic crates or bottles at the time of filling and sealing. However, this type of label offers little resistance to label damage during handling and exposure to moisture (crumpling). Furthermore, paper labels are difficult to remove from crates and tend to clog crate washers available today. After removing paper labels from plastic crates, an adhesive residue may remain on the crates.

A third technique for labelling containers, particularly glass bottles, is based on the principles described in WO 90/05088. In this publication a method of labelling bottles is described which provides a durable, highly impact resistant label and yet allows high resolution label printing. A peel-off label is provided with a removable backing layer which is reverse printed with a vinyl or acrylic ink which is dried or cured and overprinted with an adhesive. The label is applied to a container with its adhesive surface in contact therewith. The backing layer is separated from the transfer layer of the label, for example by the application of heat to either the container, the label or both. The labelled container is then provided with a coating which is subsequently dried or cured. The cured coating provides the required level of impact resistance and durability. The disadvantage of permanently applied labels is that

10 July 1997 .; J··· .··.···! .•*.WIiJlfei-Bor6& Partner

these labels, if scratched or otherwise damaged, cannot be easily removed from the bottles. Likewise, it is not possible to provide the same container with new and/or different labels each time, which is desirable for promotional activities.

The object of the present invention is to provide a transfer layer which can be easily applied to a container and removed in an environmentally friendly manner in a washing process using a washing liquid without the printing inks from the label contaminating the washing solution, such a peel-off label having good adhesion during storage and use of the container, but can be removed very quickly from the container in an economical manner in order to replace the label with new and/or different labels, while water-soluble printing inks can be used as the printing substance, which are environmentally friendly and widely used in food technology; it is further part of the object of the invention to provide a reusable crate system which can be equipped with attractive labels which can be easily and economically removed and reapplied at relatively high speeds.

According to the invention, the peel-off label for solving the problem is characterized in that the transfer layer comprises an upper and a lower protective layer on each side of the printing ink layer, the upper and lower protective layers contacting each other outside the circumference of the printing ink layer to form a closed envelope around the printing ink layer.

By enclosing the ink in the envelope between the protective layers, it is possible to remove the transfer layer from the container to which it has been applied by a wet removal process, such as a soaking process or a process using high pressure water jets. The ink is prevented from leaking out of the envelope during such a process, so that no contamination of the

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wash water. During the wet removal process, no more than 10% by weight of the ink in the transfer layer is dissolved in an alkaline wash solution. This prevents the containers from being discolored by the ink. In addition, the ink levels in the wash solution remain low enough not to affect the aerobic and anaerobic treatment in the wastewater treatment plants. The low concentrations of ink in the wash water prevent accumulation of metals in the sewage treatment plant sludge, so that this sludge does not have to be treated as chemical waste under government regulations. By simply collecting the removed labels from the wash liquid, a very economical washing process can be achieved.

Preferably, the ink layer comprises separate zones of dimensions between 0.5 mm ² and 500 cm ² , the upper protective layer and the lower protective layer contacting each other outside the separate zones to form individual enclosures around each zone of the ink layer. The areas of the transfer layer connecting the separate zones of the ink layer will have a reduced thickness compared to the zones where an ink layer is located between the protective layers. After transfer of the transfer layer to a container, it is possible that no label material is located outside the separate ink zones. These areas of reduced thickness or these open areas outside the enclosures form natural points of attack for the washing solution so that the label can be removed in individual parts. Since the washing solution has access to the label-container interface via the areas outside the enclosures around the print patterns, a very rapid removal of the transfer layer from the container is possible, with the label being removed in individual parts. These parts can be seeded out of the washing solution using conventional sieves with openings ranging in size from 0.1 mm to 10 mm, preferably around 2 mm.

Although it is preferred to use the transfer layer according to the present invention

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application on reusable plastic crates, the label can also be used in combination with plastic bottles, such as PET bottles, food trays, glass bottles or similar.

A preferred peel-off label according to the present invention comprises a transfer layer that is permeable to soaking liquids.

"Permeable" means that a transfer layer has a water absorption value after three hours of between 0.0 and 100 g/m ² , preferably around 5 g/m ² , in water at room temperature. Such labels have a water vapor transmission rate or amount or water vapor transmission between 50 and 750 g/m ² , preferably around 600 g/m ² after 24 hours for water at room temperature.

The transfer layer may comprise a cover layer covering the ink patterns, which cover layer forms the outer cover layer surface after application of the transfer layer to a container. The cover layer may be formed, for example, by an acrylic-containing wax coating. The cover layer may be a continuous layer or may be discontinuous and printed in register with the ink patterns. The acrylic-containing wax cover layer may very advantageously be penetrated, for example, by a 0.5% NaOH solution, while at the same time forming a sufficient barrier against the penetration of moisture during storage and use of the label on the container. Labels according to the present invention, which combine sufficient durability with rapid and economical removal, have a pencil hardness between 1N and 7N in the dry state and a pencil hardness less than 0.5 N after a soaking time between 1 minute and 15 minutes in water at 20 ⁰ C.

Preferably, the transfer layer has a configuration such that it tears into at least four parts under turbulent soaking conditions in an aqueous liquid having temperatures below 100 ⁰ C, preferably below 70 ⁰ C,

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with a soaking time of not more than 20 minutes, preferably not more than 10 seconds. When the transfer layer is peeled off from the container, the size of the majority of the parts that form after the transfer layer has been torn apart or broken is preferably not smaller than the dimension of the separate zones of the ink patterns. Although some of the envelopes may tear during the washing process, this will cause only a relatively small amount of leakage of the inks contained in the envelopes, since these inks will still be surrounded by a significant portion of the protective layers.

When using the protective layers according to the present invention, water-soluble inks can be used. In a preferred embodiment, the uppermost protective layer comprises an unpigmented printing ink that is compatible with the underlying printed zone. The lower protective layer preferably comprises an adhesive layer or an intermediate layer that is compatible with an underlying adhesive layer and the overlying layer of printing ink zones.

The upper protective layer can be discontinuous and printed in register with the ink pattern. In this way, the lower protective layer can be directly attacked by the washing liquid during removal of the transfer layer. If the lower protective layer is also discontinuous, the underlying adhesive layer can be directly attacked by the washing liquid. In a preferred embodiment, both protective layers and an underlying adhesive layer are discontinuous and all printed in register.

After applying the transfer layer to a container, a cover layer can be applied over the transfer layer, with the cover layer containing an acrylic wax. The acrylic wax is relatively impermeable to water, thus providing good resistance to scratching and peeling of the label during use of the container.

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Nevertheless, the acrylic wax protective layer is permeable to an aqueous alkaline solution, so that the transfer layer can be easily removed, for example from a 0.5% NaOH solution.

Preferably, the transfer layer is heat treated after it has been applied to a container to cause shrinkage of at least parts of the transfer layer. The heat treatment fuses the various layers of the peel-off label.

A label according to the present invention, which combines sufficient durability during storage and use with rapid and economical removal, has preferably been heat treated after application to the container at temperatures between 40 ⁰ C and 100 ⁰ C, more preferably between 50 ⁰ C and 90 ⁰ C.

By carefully selecting the composition of the label, the use of a protective coating and the type of post-treatment (heat treatment), it is possible to control the properties of the transfer layer, especially with regard to its behavior during washing.

The choice of adhesive used to adhere the label image to the container surface will affect the wash-off properties. The adhesive must have been activated before or during application of the transfer layer to the container. A simple and generally preferred method of attaching the image is to use heat-activated adhesives applied to the image in the form of an inverse printed label. Other methods include the use of adhesives that can be activated by radiation, chemicals, electron beam, microwaves, UV and the like. It is also possible to use adhesives that can be activated by photochemical initiation, moisture, enzymatic action, pressure or ultrasonic treatment.

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A preferred adhesive has a low adhesion temperature, preferably between 60 ⁰ C and 90 ⁰ C, more preferably between 50 ⁰ C and 90 ⁰ C. Instead of a separate layer of adhesive, it is also possible to use a printing ink in the transfer layer which itself has adhesive properties after activation.

Preferably, the attachment surface of the container to receive the transfer layer has a surface tension of at least 0.6 mN per cm (60 dynes per cm).

A transfer layer according to the present invention can be removed using conventional crate washing equipment in which the label parts can be removed from the soaking solution by sieving. Since no parts of the label dissolve in the soaking solution, no special treatment equipment is necessary to clean the washing solution.

Embodiments of a transfer label or a peel-off label according to the invention as well as a washing method are described in detail below with reference to the accompanying drawings, for example. In the drawings:

Fig. 1 a heat transfer label according to the invention, in which separate printing

colour samples are each contained in an individual wrapping,

Fig. 2 shows a washing device for removing a transfer layer according to the present invention from a container, in particular from a plastic box,

Fig. 3 is a cross-sectional view of the washing device according to Fig. 2

along the line lll-lll,

Fig. 4-7 various embodiments of the transfer layer of a peel-off label according to the present invention,

Fig. 8 schematically shows a plan view of an embodiment of a peel-off label according to the invention with different sized covers around the printing inks

pattern,

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Fig. 9 schematically shows a method of applying the transfer layer according to the present invention to a reusable box, and

Fig. 10 and 11 graphically show the removal time of a transfer layer at different post-heating temperatures without and with a wax protection layer. 5

Fig. 1 shows an embodiment of a transfer label or a transfer inscription or peel-off label 1 according to the present invention with a carrier or support layer or layer 2, which is formed, for example, from an approximately 50//m (2-mil) thick polypropylene film. A silicone layer 3 is located on the carrier or support layer 2. A transfer layer 4 is arranged on the silicone layer 3, which consists of an upper surrounding layer or security layer or protective layer 5, 5', an ink layer 7, 7', a lower surrounding layer or security layer or protective layer 6, 6' and an adhesive layer 8, 8'.

After applying the release or transfer layer 4 to a container, the carrier layer 2 and the silicone layer 3 are removed using heat and pressure. The adhesive layer 8 bonds the transfer layer 4 to an underlying container surface and the outward-facing layer is formed by the upper protective layer 5, 5'.

The label carrier 2 provided with the electron beam cured silicone layer 3 may be, for example, a polypropylene film of 25 to 75 μηι (1-3 mils) thickness, as offered by Mobil Chemical, Films Division, Rochester, New York. Before printing the top protective layer 5, 5' onto the silicone layer 3, the silicone surface must be corona treated. Corona treatment allows uniform wetting of the printing materials and also allows release of the transfer layer 4. Preferably, corona treatment is performed on the carrier layer 2 and the silicone layer 3 just before the first print of the top protective layer 5 is applied. A desired treatment level should be approximately 30% of 3.5 kW.

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During handling of the silicone coated carrier layer 2, care must be taken not to scratch the silicone layer 3. Scratching the silicone layer 3 would allow the upper enclosing layer 5 to come into contact with and adhere to the underlying polypropylene film 2, which would hinder the transfer of the transfer layer 4 during application.

would adversely affect.

The upper protective layer 5, 5' consists, for example, of unpigmented printing ink and has several functions. Firstly, it slows down or prevents the penetration of water into the underlying printing ink layer 7, 7'. Since the layer 5, 5' is printed wider than the underlying color pattern 7, T, it forms part of a coating which completely surrounds the colored printing ink layers 1, T. Furthermore, the upper protective layer 5, 5' provides a consistent medium between the printing inks and the release surface 3 made of silicone. The layer 5, 5' is very important for the overall transferability of the label or label carrier and should be applied with a weight of at least 1.4 g/m ² . It is important that after the upper protective layer 5, 5' has been applied, this layer is free of air bubbles and craters or pores. Furthermore, the upper protective layer must be dry before the following

20 de printing ink layer 7, 7' is printed on it.

After printing the top protective layer 5, 5' onto the release layer 3, an optimum peel force of 1 N (100 g) or less should be measured in a standard tape peel test. Within five hours of application, the peel force of the top protective layer will be reduced by approximately 60% or 0.4 N (40 g). With the specified peel force, the protective layer 5 should be completely removed. A suitable material for the top protective layer 51 is available from Environmental Inks and Coatings, Morganton, North Carolina under the type number 1304.

Examples of a preferred ink for the ink layer 7, 7' include a waterborne organic substance such as is available from Environ-

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mental Inks and Coatings, Morganton, North Carolina under the type number Aqua BW EH-31721, EH 5301 6, EH 90967. These printing inks have a high stability, even at temperatures above 200 ⁰ C without discoloration or loss of adhesion.
5

The lower protective layer 6, 6' provides a strong bond between the adhesive layer 8, 8' and the colored ink layers 7, T. It is formulated to chemically anchor to the ink and provide excellent wetting and bonding of the adhesive layer. The lower protective layer 6, 6' bonds to the upper protective layer 5, 5' outside the ink layer 7, T in such a way that a closed envelope is formed around the separate ink patterns 7, 7'. A suitable material for the lower protective layer 6, 6' is available from Environmental Inks and Coatings under the type number XP 11358.

The adhesive layer 8, 8' may be formed by a waterborne organic material which is printed in a number of consecutive flexography stations, such as three stations, or may be dip coated on a single station. The adhesive layer 8, 8' may also be applied by a single gravure station. Preferably, the adhesive layer is heat activated and has a low tacking temperature of 80 ^° C to 107 ^° C. The preferred adhesive mass is about 3.5 g/m ² .

The layers of transfer layer 4 can be applied in a FIxography printing press with up to ten printing stations. Five stations can

be used to print the layers 5, 5', 6, 6' and the adhesive layer 8, 8', which may consist of three separate adhesive layers. Five types of colored ink 7, 7' can be applied using the remaining five flexographic printing stations.
30

Instead of a flexographic printing process, a gravure press equipped with a Korana treatment device can also be used. Since the

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Material deposition is heavier than in a flexography process, only three gravure stations would be necessary to apply the protective layers 5, 5' and 6, 6' and the adhesive layer 8, 8'.

Furthermore, rotary screen printing processes can be used to apply the layers 5, 5', 6, 6' and 8, 8'. After printing the lower protective layer, care must be taken to ensure that it extends beyond the perimeter of the printing ink patterns 7, 7', but remains within the perimeter of the upper protective layer 5, 5'. Preferably, the adhesive layer 8, 8' extends beyond the perimeter of the lower protective layer and is equal to the perimeter of the upper protective layer.

layer 5, 5' adjusted.

Fig. 2 shows a schematic side view of a crate washing device for removing the transfer layers according to the present invention from crates 12 fed to the crate washer 10 via a conveyor belt 11. The crates 12 are first transported to a pre-rinse station 13 and sprayed with a pre-rinse solution applied via a number of nozzles 14 arranged above and below the conveyor belt 11. The speed of the conveyor belt 11 is such that the residence time of the crate 12 in the pre-rinse station is between 6 and 8 seconds. The temperature of the pre-rinse solution is 60 ⁰ C. The pre-rinse solution preferably contains 0.5% NaOH solution.

After passing through the pre-rinse station 13, the crates are transported through a soaking station 15 via a sloping section 16 of the conveyor belt 11. The dwell time of the crate in the soaking station is between 10 and 40 seconds. In the soaking station, the crate is completely submerged and the soaking solution is circulated in the soaking station 15 by nozzle means 35 to cause turbulent soaking conditions. The turbulent soaking conditions may include, for example, the liquid being circulated from the soaking station 15 via the nozzles 35 at a rate or velocity or amount or

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Amount of 60 m ³ /h for a total volume of soaking solution of 5 m ³ . It is important that the transfer layers are completely removed from the boxes 12 in the soaking station 1 5 without any parts remaining on the boxes. Such remaining parts would, when dried, adhere firmly to the boxes and cause undesirable contamination of the box surface.

form.

From the soaking station 15, the crates are transported to a rinsing station via an upwardly running transport track or conveyor 17. The rinsing solution can contain water at a temperature of 30 ⁰ C. The dwell time of the crates in the rinsing station 18 is between 6 and 13 seconds.

Connected to each rinse station 13, 18 and to the soaking station 15 are screen sections 20, 21 and 22. Each screen section includes a rotating screen belt 23, 24, 25 driven by motors 26, 27 and 28 respectively. Pumps 29, 30 and 31 direct the rinse solution and the soaking solution from each respective station through the rotating screen belts at a rate of, for example, 60 nrvVh. The screened liquids are circulated back to the nozzles 14 and 19 in the pre-rinse and post-rinse stations 13, 18 respectively and to the soaking station 15.

Fig. 3 shows a cross-sectional view along the line iii-iii in Fig. 2. It can be seen that the screen belt 24 rotates around two rollers 37, 38. The upper end of the screen belt 24 extends above the level of the soaking solution in the soaking station 15. The screen belt 24 comprises a two-layer belt-shaped screen element with a mesh size of 2 mm. During operation it is important to rotate the screen belt 24 continuously in order to prevent the label pieces from the transfer layers which break into pieces in the soaking station from clogging the screen belt. A spray nozzle 39 cleans the surface of the belt-shaped screen element by high pressure water or air jets. The removed label pieces are collected in a collection area 40.

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It has been found that a very efficient removal of the labels from the boxes 12 is achieved using 0.5% NaOH solution in the pre-rinse station 13 and the soaking station 15. However, it is also possible to apply a pre-processing material to the labels before they enter the box washer 10, which causes a softening of the labels before entering the box washer. For example, a surface-active component can be sprayed onto the boxes 12 as they move towards the box washer 10. It is also possible to apply a gel-like material with a chemical composition that begins to attack the label before entering the box washer 10. In such a case, it may be possible to use only water in the box washer 10, instead of an alkaline solution.

Fig. 4 shows an alternative embodiment of a peel-off label according to the invention, comprising a backing layer 48, a silicone release layer 49 and a transfer layer 50. The ink layer 52 of the transfer layer 50 is a continuous layer, for example having a dimension of 10 by 10 centimeters. The upper protective layer 51 and the lower protective layer 53 enclose the ink layer 52 and engage each other around the periphery of the ink layer. In doing so, a single envelope is formed around the ink layer 52. During removal of the transfer layer 50 from a container to which it has been applied, the transfer layer 50 may tear into several pieces. In doing so, the envelope formed by the upper and lower protective layers 51, 53 is torn. Nevertheless, it has been found that sufficient enclosure is still provided in this case to prevent the inks

layer 53 dissolves in the washing solution.

In the embodiment shown in Fig. 5, the ink layer 52 is formed or constructed of separate zones 52, 52'. Each zone of the ink layer can be formed, for example, by individual letters, individual sentences or individual word blocks. The individual zones 52, 52' can also be formed by other graphic objects. As shown, the upper

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Protective layer 51 the lower protective layer 53 along the circumference of each individual printing ink zone 52, 52' or is connected to it or adheres to it. In this case, envelopes are formed around each individual printing ink zone and efficient wrapping is possible.
5

In the embodiment shown in Fig. 6, the upper protective layer 51 is formed by separate zones 51, 51'. The open areas between the separate zones of the upper protective layer 51, 51' allow the washing solution to easily penetrate and attack the underlying protective layers 53 and adhesive layer 54.

As shown in Fig. 7, the adhesive layer 54, the lower protective layer 53, the ink layer 52 and the upper protective layer 51 are each printed in register and form separate zones 51, 51', 52, 52', 53, 53' and 54, 54'. Such a transfer layer has a very attractive appearance and the container surface is clearly visible between the respective individual ink zones 52, 52'. With this specific construction, a very fast washability or washability is achieved, since the washing liquid can very quickly attack the adhesive layer 54, 54' by passing through the open areas between

20 see the individual printing ink zones 52, 52'.

As shown in Fig. 8, a transfer layer according to the present invention may comprise several parts. For example, a graphic object 55 such as an image may consist of a single layer of ink enclosed around its periphery 55' between an upper and lower protective layer of a structure as shown in Fig. 4. Instead of the graphic object 55, separate lines of text 56 may be enclosed between an upper and lower protective layer, for example with a structure according to Fig. 5, Fig. 6 or Fig. 7. As indicated at 58, individual letters in a sentence may be individually

30 be enclosed between an upper and lower protective layer.

Fig. 9 shows a schematic view of the application process of a trans-

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fer layer of a transfer label according to the invention on a reusable box 59.

The label application process will now be described in order of progress. Station 60 shows the step of surface treatment and temperature stabilization by means of a preheating treatment using a flame heater or burner 60'. To effect adhesion of two polymeric materials, many factors must be taken into account, such as cleanliness, pressure, temperature, contact time, surface roughness, movement during bonding and adhesive film thickness. An additional important consideration is critical surface tension. The generally accepted method of measuring critical surface tension is with a dyne solution, which is well known. For most adhesive applications, the critical surface tension for polyethylene is 0.31 mN (31 dynes) per centimeter. A series of tests were conducted which showed that for the best adhesion of the adhesive described above to a polyethylene surface, a treatment level of 0.6 to 0.7 mN (60 to 70 dynes) per centimeter was necessary. Further testing of commercially available equipment showed that flame treatment optimized both capital costs, operating costs, and the time required to achieve the critical surface treatment required.

In order to achieve and maintain rapid adhesion for the adhesive, it is necessary to heat the polyethylene box 59 at station 61 before the label adhesive contacts it. To prevent distortion of the box, it is desirable not to heat the surface above 93 ⁰ C (200 ⁰ F). Since the surface temperature upon exiting flame processing is approximately 52 ° C (125 ° F), it is necessary to heat the surface to approximately 24 ⁰ C (75 ⁰ F) at station 61. Again, many options are available for warming. Hot air, additional flame heaters, gas fired infrared panels and electric ceramic panels have all been tested and found to be either too

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slow or difficult to control. It was found that an electrically heated flat quartz glass emitter plate 61' with zoned band control for localized label transfer provides the maximum free air transfer of infrared energy without the effects of surrounding environmental factors. With an emissivity of 0.9 for polyethylene, a desired emitter plate temperature of 90O ⁰ C (1652 ⁰ F) and 94O ⁰ C (1275 ⁰ F) emits the most efficient wavelength (2.5 to 3.2 pm) of infrared energy for peak absorption. The unit tested had a power rating of 9 to 10 and 9.5 watts per cm ² (60 watts per inch ² ), respectively. The time to heat the polyethylene surface to the necessary 24 ⁰ C (75 ⁰ F) was 4.5 seconds at a distance of 2.5 centimeters from the emitter plate.

Station 62 illustrates the method of label application whereby the printed ink materials are transferred from the polyethylene film carrier material to the polyethylene surface using the tactile properties of the heat activated adhesive to overcome the bond of the transfer layer to the corona treated silicone coating. The factors affecting transfer are contact time, temperature and pressure applied during contact, and the film tension during contact, especially the tension of the film after ink release. The diameter of the pressure roller 63 is also an influencing factor but not a variable. For this application the roller diameter is 38 mm. The roller is made of a silicone rubber over a steel core, with a rubber durometer reading of 50 Shore A to 80 Shore A. It should be noted that deformation (flattening) of the rubber roller is less at higher durometer, thus the contact area is smaller and the transfer pressure is greater. This is important at higher line speeds where contact time is minimized. A box moving at 18.3 meters per minute (60 feet per minute) behind a 38 mm diameter roller will therefore have a contact time of 1 millisecond per 1 degree of roller rotation, with no roller deformation.

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The roll pressure is applied by a pneumatic cylinder 64 which is activated by a conventional electromagnetic valve or solenoid valve which in turn is operated by two (2) proximity switches, one for advancing the roll and the other for retracting it. Other devices, such as mechanical linkages, are obvious and are not listed here. The pressure is distributed along the length of the cylinder and for this particular label, transfer ranges of 12 to 17 kilograms per centimeter of roll length are desirable.

Consequently, the invention results in the film being fed at exactly the same rate as the box passes behind the roller, due to the heat activated adhesive adhering to the high energy box surface. The pressure roller 63, which rotates freely, maintains the same tangential speed as the linear speed of the film and box. Consequently, the ink is completely transferred without deformation.

distortion transmitted.

For rapid and complete adhesion, the pressure roller 63 is fabricated around a hollow core. Suspended within the hollow core is a resistive heating element which is operated by a control device. The heating element, rated at 500 W, can maintain the roller surface at any predetermined temperature. For purposes of the invention, the temperature of the roller surface is between 120 ⁰ C and 190 ⁰ C (250 ⁰ F and 370 ⁰ F).

Many silicone coated polymer films can be used for the printed carrier. High temperature films such as polyester can be used in continuous contact with the heated roll. Low temperature films such as polypropylene must be kept from contacting the heated roll during pauses in the labeling process. To achieve this, film guides 65 are used to hold or support the film as the roll is retracted. The guides 65 are mounted to be spaced

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approximately 13 mm between the guides and the labeled surface. At the same time, the roll is retracted approximately 1 3 mm behind the film. By maintaining these distances, stretching and deformation of the film as with polypropylene is avoided. High temperature films would not require the guides.

It has also been found that film tension, especially on the film exit side of the roll, is important to complete the ink transfer. Through experimentation it has been found that a continuous tension of approximately 25 N (2.5 kilograms) is useful. This is achieved by a spring-loaded dancer arrangement of arm and roll.

Conventional gripper rollers and stepper motors are used to transport and precisely position the film to the next label, using a printed mark to trigger an optical scanning device.

Protection of the ink against scratching from careless handling as well as against damage to its weather resistance when subjected to outdoor storage is achieved by applying an acrylic-based wax-water emulsion at station 66. This is applied by an applicator roller 68 which is supplied with a controlled amount of coating material from a wet roller. Control is achieved by means of a squeegee device. The coating extends well over the edges of the ink pattern and seals the edges against moisture penetration.

The final process step is the joining or combining of the layers of coating, label ink and adhesive at station 67 by a flame heating device 67' and also the interdiffusion of the adhesive layer with the polyethylene carrier formed by the box 59. This knowledge was gained through extensive testing of many heating systems. Just as flame treatment was recognized as the best technique that achieves the desired

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surface energy for label adhesion, it was recognized that flame treatment of the label and coating composite was the best technique to develop the desired resistance to water immersion without sacrificing mechanical properties or altering the visual properties of the applied label or deforming the polypropylene box 59.

To illustrate the numerous properties that affect the adhesion and washability of the preferred transfer layer of the present invention, the following tests were conducted, including a wash test, a pencil scratch test, a water uptake/release test, and a water vapor transmission test as described below.

Washing test

To find the optimum washing conditions for a label according to the present invention, a transfer layer 50 having a configuration as shown in Fig. 4 was applied to a polyethylene box. The dimensions of the label were approximately 10 by 10 centimeters and the adhesive layer 54 was 100% urethane adhesive with an adhesion temperature of 79°C. The labels were applied to the box with a roller temperature 63 in Fig. 9 of 155°C at a roller pressure of 2.5 bar. The preheat temperature of the box (in stations 60 and 61 in Fig. 9) was 75 ^° C. The speed of the boxes 59 through the label application unit was 40 boxes per minute. To determine the influence of the post-heat temperature at which the boxes were heated after label application at station 67 in Fig. 9, post-heat temperatures of 4O ⁰ C, 65°C and 90 ⁰ C were used. After label application, the boxes were stored for at least 24 hours at a temperature of 20 ⁰ C. The boxes to which a label was applied were then soaked in a 0.5% NaOH solution at temperatures of 2O ⁰ C, 5O ⁰ C and 7O ⁰ C.

&Lgr;0. JuU 1397 .I I*" .·*.*♦': M5lier-%o?l& Partner

The soaking of the boxes was carried out in a soaking bath of 20 litres without turbulence, with a soaking time (10-50 seconds) such that after spraying the soaked box with a shower head at a rate or quantity of 6 litres/minute, the label is completely removed within 2 seconds.

A second set of boxes was prepared in such a way that after label application a protective layer of wax was applied, as in station 66 in Fig. 9.

The results of the soaking times required for label removal within 2 seconds versus post-processing temperature are given in Tables I and II. From Table I, the results of which are graphically shown in Fig. 10, it can be seen that for labels to which no wax coating has been applied, the soaking time decreases dramatically for soaking solution temperatures above 2O ⁰ C. For post-processing temperatures of 9O ⁰ C, the durability of the label was increased and the soaking time remained above 5 seconds.

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Table I Box washing test (no wax layer applied)

Residual heat 0.5% pickling agent! Time Time Time Average T ( ⁰ C) (lake) (lake) (lake) !lake) ( ⁰ C) no 90 120 105 20 40 180 150 165 65 210 240 225 90 480 420 450 no 2 2 2 2 50 40 3 3 3 3 65 3 3 4 3.3 90 15 14 13 14 no 1 1 1 1 70 40 1 1 1 1 65 1 1 1 1 90 6 6 7 6.3

It was found that an optimum post-heat temperature was between 65°C and 90 ^° C. At post-heat temperatures below 65°C, too little coalescence of the applied transfer layers was achieved, so that the applied transfer layers had insufficient durability and were too easily removed during storage and use. At post-heat temperatures above 90 ^° C, the durability of the transfer layer became too great and short removal times could not be achieved in an economically feasible manner. During the spray period with the shower head, it was observed that after soaking, the labels detached from the box and broke into several (2 to 4) pieces.

If, prior to the flame treatment step at station 67 in Fig. 9, a wax layer is applied at station 66, the durability of the labels is improved and the soaking times are increased. From Table II it can be seen that for 0.5%

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Mu!iar-*Bor» & Partner

pickling solution the wax layer leads to longer soaking times. The results from Table M are shown graphically in Fig. 11.

Table II Box washing test (wax layer applied)

Residual heat 0.5% pickling agent! Time Time Time Average T ( ⁰ C) (lake) (lake) (lake) (lake) ( ⁰ C) no 150 150 150 20 40 180 180 180 65 300 270 285 90 <600 600 no 4 4 5 4.3 50 40 6 6 6 6 65 7 7 8th 7.3 90 13 14 16 14.3 no 2 2 3 2.3 70 40 2 2 2 2 65 2 2 2 2 90 6 6 7 6.3

It was observed that when attempting to remove the labels, as in the washing test described above, using high-pressure water jets alone at 20 ⁰ C and a pressure of 120 bar, at a conveying speed of 15 meters per minute and a spray angle of 90° from a distance of 10 centimeters, no label removal was achieved. Even for labels without any wax coating and without post-heat treatment, no removal by high-pressure water jet media was possible.

Pen scratch test

The purpose of the pen scratch test is to determine the minimum and maximum resistance of the

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Labels that can be obtained by taking various measures, such as using a protective wax layer and heat treatment to cause the label layers to bond. Boxes of labels applied at different post-heat temperatures, with and without wax, have been tested.

The labels were the same labels used in the washing test described above and were applied to the boxes under the same conditions.
10

The pen scratch test was performed using a "scare resistance test model 435" supplied by Erichsen (P.O. Box 720, D-5870 Hemer, Germany).

During the scratch test, a pen with a plastic insert was used to scratch the label horizontally in the middle at an angle of 90°.

After application of the label, the boxes were stored for at least 24 hours at a temperature of 20 ⁰ C. Before scratching, the boxes were soaked in water without turbulence at 2O ⁰ C. The results of the scratch test are given in Table III and Table IV, in which the scratch results are given in N

are specified.

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·· · · · · Muller-BoräS Partner

I&diams;

25

Table Hl

Pen scratch test (in N)

Label without wax coating

Post-heat
temperature
( ⁰ C) Soaking time (min) 0.5 1 1.5 2 2.5 3 3.5 0.4 0.2 0.1 no 0.3 0.2 0.1 0.9 0.2 0.1 40 0.7 0.2 0.1 0.7 0.2 0.1 65 0.5 0.1 0.1 1.2 0.8 0.6 0.6 0.4 0.2 0.1 90 1 0.8 0.6 0.5 0.3 0.2 0.1 0 1 1 1.3 1.1 1.1 1 1.5 1.1

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26

Table IV

Pen scratch test (in N)

Label with wax coating

Residual heat 0 0.5 1 1.5 Soaking
Time 2.5 3 4 5 6 7 8th 9 10 ( ⁰ C) (min) 5 3 1.4 0.5 2 0.2 0.1 5 3 1.5 0.7 0.2 0.1 no 0.3 5 2.8 1.3 0.4 0.4 0.1 5 3 1.4 0.6 0.2 0.1 40 0.3 5 2.5 1.2 0.5 0.4 0.2 0.1 5 2.9 1.3 0.5 0.1 65 0.3 5 4 2.5 1.3 0.2 0.7 0.6 0.4 0.4 0.4 0.3 0.3 0.3 0.3 5 1 2.8 1.5 0.7 0.5 0.3 0.3 0.3 0.2 0.2 0.2 0.2 90 0.7 0.8

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& Partner

From Tables III and IV it can be seen that the post-heat flame treatment does not appear to significantly affect the scratch resistance of the transfer layers in the dried state. However, the durability of the transfer layers is increased by the post-heat flame treatment as can be seen from the higher pen hardness after soaking. From Table IV it can be seen that the application of a wax layer covering the label significantly increases the scratch resistance of the label. It was found that for high post-heat flame treatment temperatures of 110 ⁰ C in combination with a wax coating a scratch force of 8 Newtons is achieved. Labels with a pen hardness of 8 Newtons are considered semi-permanent and cannot be removed in an economically feasible manner.

Problems also occurred during labeling at post-heat temperatures above 90°, as at these temperatures the polyethylene boxes became brittle after just a few applications, the box pigments, it was found, discolored and deformations of the softened boxes on the conveyor and palletizer were seen.

At a post-heat temperature below 65°C, the strength of the labels was found to be insufficient for labels that did not have a wax coating. For labels without a wax coating, the target pen hardness in the dry state should be around 1.2 N and the soaking time until the scratch force drops below 0.3 Newton should be less than 3 minutes. For a wax-coated label, the target scratch force should be around 5 Newton in the dry state and the soaking time until the scratch force drops below 0.3 Newton should be less than 10 minutes. Transfer layers that have the above properties were found to have an optimal combination of durability and washability.

30

Water absorption test

The labels according to the present invention can be easily removed from a container

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*···· * J ·* Wull|r-Bor6 & Partner

removed, particularly from a plastic box, due to their specific water permeability which allows the softening solution to penetrate the label and subsequently tear the label into pieces and detach it from the container. Preferred labels have been found to have a water absorption of around 5 g/m ² after 3 hours in a water absorption test as described below. Labels according to the invention have a water absorption value greater than 0 and less than 100 g/m ² in 3 hours. The water release of a preferred label was 4.5 g/m ² in 30 minutes in the water release test as described below. Preferred labels according to the present invention have a water release value greater than 0 (a complete barrier) and less than 100 g/m ² after 3 hours.

Two samples were prepared, each sample with 2 labeins of a respective thickness of 12.7 pm (12.7 microns) at 22.4 ⁰ C and 48% relative humidity, each

5 Sample with a surface area of 85.8 cm ² . For each sample two labels were

applied to a single piece of clear glass measuring approximately 8 cm * 23 cm * 0.05 cm (3 inch * 9 inch * 0.02 inch). Due to the extremely light weight of the labels, it was necessary to apply two labels per piece of glass to obtain a weight detectable within a range of a two decimal place electronic gram scale. The samples were prepared as follows: The glass slides were carefully cleaned and placed in a heating oven until an approximate temperature of 120 ⁰ C (250°F) was reached on the glass surface. The glass was then removed from the heating oven and placed on a silicone rubber mat. A label was immediately placed on the glass and secured to the surface using a silicone roller. Roll pressure was continuously applied to the full length of the label until all trapped air was removed (about 5-6 back and forth strokes). After the glass had cooled, the carrier film was removed. The opposite side of the glass plate was then labelled by heating a clean aluminium plate (slightly larger than the glass plate) to about 12O ⁰ C (250°F) in a convection oven, then placing the glass on the surface

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of the aluminum plate {label surface down), allowing the heating of the top glass surface. The label was then applied and held in position by the silicone roller described above. Once again, when the glass has cooled, the carrier film is removed. Next, a wax coating with a dry weight of 0.043 g was applied to the surface of both labels. In the final step, using a propane oxidation flame, both labels were subjected to a flame treatment by rapidly moving the flame across the outer surface of the label samples. Once the label samples had then cooled, the labels were ready for the water absorption test.

A stainless steel immersion tank 33.66 cm in diameter and 24.13 cm in height was filled with deionized water. Care was taken to ensure that the water level was deep enough to allow complete submersion of the sample. The sample was placed with the short extension perpendicular to the bottom of the tank. The glass slides were placed on a thin wire frame in the immersion tank. A thermocouple was placed inside the water immersion tank. After each time interval as indicated in Table V, the sample was removed from the tank, excess surface water was blotted off, the sample was weighed and placed back in the tank. This procedure was continued for the duration of the test. The results are shown in Table V. Sample 1 reached its maximum absorbance of 0.04 g at the 3 hour mark and maintained this value until the 5 hour mark before losing its ability to hold water at this level.

After the 5 hour period, the label lost its ability to hold water. We believe this phenomenon was caused by structural degradation of the label. Sample 2 also reached its maximum absorbance of 0.04 g at the 3 hour mark. At the 5 hour mark, further testing of this sample was terminated in preparation for the water release test described below.

From the water absorption test it can be concluded that a preferred

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Label with a thickness of 12.7//m {12.7 microns) has a water absorption capacity of 0.04g/85.8 cm ² or approximately 5g/m ² after 3 hours at room temperature.

Table V
Water absorption test

Time Sample 1
Weight in
grams Sample 2
Weight in
grams Relative
humidity
(%) Water temperature
ture in the tank
( ⁰ C) Indoor air
Temperature
( ⁰ C) 8:00 am. 59.77 59.77 47 21.7(71 ⁰ F) 22.4 (72.4 ⁰ F) 8:10 a.m. 59.80 59.80 47 21.7(71 ⁰ F) 22.4 (72.4 ⁰ F) 9:00 am. 59.81 59.81 47 21.7(71 ⁰ F) 22.4(72.4 ⁰ F) 10:00 am. 59.83 59.83 47 21.7 (71 ⁰ F) 22.4 (72.4 ⁰ F) 11:00 a.m. 59.85 59.85 48 22.2 (72 ⁰ F) 22.4 (72.4 ⁰ F) 12:00 am. 59.85 59.85 48 22.2 (72 ⁰ F) 22.6 (72.6 ⁰ F) 1:00 p.m. 59.85 48 22.2 (72 ⁰ F) 22.6 (72.6 ⁰ F) 2:00 p.m. 59.84 48 22.2 (72 ⁰ F) 22.6 (72.6 ⁰ F) 3:00 p.m. 59.81 49 22.2 (72 ⁰ F) 22.6 (72.6 ⁰ F)

To calculate individual label gram weights from the data in Table V, refer to the following:

Each sample involves the use of two labs. To calculate the weight of Sample 1 at 1:00 p.m., subtract the reading at 8:00 a.m. from the reading at 1:00 p.m. and divide by 2. For example:

read at 1:00 pm: 59.85
read at 8:00 am: - 59,77

0.08 / 2 = 0.04g

Water release test

Immediately after completion of the above water absorption test, Sample 2, prepared as above, was subjected to the water release test. The sample was blotted to remove excess water, weighed and the values recorded. The sample was first exposed to ambient temperature for

July 10, 1997

*« · .. · · · MüJfer-Bor* & Partner

for half an hour and weighed. Half an hour after weighing the sample, it was placed in a preheated (53' ⁰ C) test oven (small electrically heated oven, Quieny Lab Inc., Mode! 20 Laboratory Oven or equivalent). The sample was left in the oven for over one hour and weighed. After that, the sample was returned to the oven and left there for 3.5 hours.

From Table VI it can be concluded that the water absorbed by Sample 2 was released in 30 minutes while exposed to ambient room temperature and humidity (48%). In fact, the sample was found to lose 0.01 g of its original weight, which may be seen as an indication that the label was not thoroughly dried during application. Thus, a preferred label of 85.8 ^cm2 size and 12.7 microns (12.7 microns) thickness has a water release of more than 0 and less than 0.1 g/24 hours with a peak release of 0.045 g in 30 minutes under these given parameters.

Table V!
Water release test

Time Sample 2
Weight in grams Room temperature
( ⁰ C) Relative
humidity Oven
temperature
( ⁰ C) 12:00 p.m. 59.85 22.55 (72.6 ⁰ F) 48 53.5 12:30 p.m. 59.76 22.55 (72.6 ⁰ F) 48 53.7 1:30 p.m. 59.76 52.3 Next reading 5:00
at the 59.76 53.0

Test of water vapor transmission rate or quantity

The optimum combination of durability and washability of the label according to the invention depends at least in part on the permeability of the label to the soaking solution. A sample of the transfer layer of the same type as tested in the water absorption/release test, with a thickness of 12.7//m, was tested for water vapor permeability. A 25 milliliter glass jar

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with a 15.9 mm diameter circular opening was cleaned with acetone and filled with approximately 10 ml of deionized or demineralized water. The opening area of the vessel was heated to approximately 48 ⁰ C (118 ⁰ F) and a circular segment of the transfer layer was firmly attached using a small piece of silicone rubber as a pressure pad. After the vessel/label had cooled, the backing film was carefully removed. Sample preparation was completed by adding a wax coating (0.001 g over the 1.99 cm ² surface area) and air drying. A second glass vessel with the same dimensions as described above was thoroughly cleaned with acetone and filled with 10 ml of deionized or demineralized water. The opening area for the sample was also heated. This sample was used as a control sample. The complete samples were weighed at various intervals over a period of 26.6 hours. The water vapor transmission rate over the entire time of the experiment was found to be 568.75 g/m ² in a period of 24 hours at 22.2 ⁰ C and 46% relative humidity. It was found that a steady state of the water vapor transmission rate was not reached until 28 minutes had elapsed from time 0. Using the steady state values after 28 minutes from time 0, the water vapor transmission rate was found to be approximately 526.93 g/m ² in 24 hours.

For the control sample without label, a water vapor transmission rate for the entire duration of the experiment was found to be 1085.7 g/m ² in 24 hours. The water vapor transmission rate of the preferred label according to the present invention will be between 50 g/m ² and 750 g/m ² after 24 hours (22.2 ⁰ C, 44% relative humidity), preferably around 500 g/m ² after 24 hours.

Claims (1)

Expectations 1. Transfer label or peel-off label (1) with a support layer (2) and a transfer layer (4) which is removably attached to the support layer (2) and comprises a printing ink layer (7), characterized in that the transfer layer (4) comprises an upper or lower protective layer (5, 6) on each side of the printing ink layer (7), the upper and lower protective layers (5, 6) touch each other outside the circumference of the printing ink layer (7) in order to form a closed envelope around the printing ink layer (7). 2. A release liner (1) according to claim 1, wherein the ink layer (7) comprises separate zones (52) having dimensions between 0.5 mm ² and 500 cm ² , the upper protective layer (5) and the lower protective layer (6) contacting each other outside the separate zones (52) to form individual enclosures around each zone (52) of the ink layer (7). 3. Peel-off label (1) according to claim 1, wherein the plurality of envelopes around the separate zones (52) of the ink pattern (7) remain closed when removing the transfer layer (4) applied to the container (59) from the container (59) in a washing process using a washing liquid. 4. A transfer film (1) according to claim 3, wherein the transfer layer (4) breaks down into at least 4 parts in the washing process under turbulent soaking conditions in an aqueous liquid having a temperature below 100 ⁰ C, preferably below 70 ⁰ C, with a soaking time of July 14, 1997 & Partner not more than 20 minutes, preferably not more than 10 seconds, and is detached from the container (59), wherein the size of the majority of the parts formed after the disintegration of the transfer layer (4) is not smaller than the dimensions of the separate zones (52) of the printing ink pattern (7).
5 5. Peel-off label (1) according to one of the preceding claims, in which the printing ink is water-soluble. 6. Peel-off label (1) according to one of the preceding claims, in which the upper protective layer (5) comprises an unpigmented printing ink, the lower protective layer (6) comprises an adhesive. 7. Peel-off label (1) according to one of the preceding claims, in which the upper protective layer (5) is discontinuous and is arranged congruently with the printing ink pattern (7). 8. Peel-off label (1) according to one of the preceding claims, in which the lower protective layer (6) is discontinuous. 9. Peel-off label (1) according to one of the preceding claims, in which the transfer layer (4) outside the separate zones (52) of the printing ink pattern (7) is permeable to the soaking liquid, 10. A peel-off sheet (1) according to any one of the preceding claims, in which the transfer layer (4) comprises an adhesive layer (8) whose adhesion is at least reduced after contact with the soaking solution, preferably by dissolving in the soaking liquid. 11. Peel-off label (1) according to claim 10, in which the adhesive layer (8) is discontinuous and is arranged congruently with the printing ink pattern (7). net is. July 14, 1997 &bull; ···· ·· ···· Garbage*i*Bcf*&Phi; partner 12. Peel-off label (1) according to claim 3 or 4, wherein the soaking solution is an aqueous, basic solution. 13. Peel-off label (1) according to one of the preceding claims with a thickness of less than 30 micrometers, preferably less than 20 micrometers, and a weight of the protective layers (5, 6) between 1 g/m ² and 10 g/m ² . 14. A peelable tape (1) according to any one of the preceding claims, comprising an adhesive layer (8) having a weight between 1 and 10 g/m ² , preferably between 3 and 7 g/m ² . 15. A release liner (1) according to any one of the preceding claims, wherein the adhesive layer (8) comprises at least two sub-layers, the adhesion of the sub-layer which is closest to a container (59) after attachment to the container (59) has a lower adhesion than the layer of adhesive which is further away from the container (59). 16. Container (59) with a transfer layer (4) applied using a peel-off label (1) according to one of the preceding claims. 17. A container (59) according to claim 16, wherein a cover layer is applied over the transfer layer (4), the cover layer comprising an acrylic wax. 18. Container (59) according to claim 17, wherein the cover layer is applied during or after application of the transfer layer (4) to the container (59). 19. Container (59) according to claim 16, 17 or 18, wherein the transfer layer (4) has been heat treated after application to the container (59) at a temperature between 40 ⁰ C and 100 ⁰ C, preferably between 50 ⁰ C and 90 ⁰ C. July 14, 1997 -Mülle»-Bor£<S» Partner 20. Container (59) according to one of claims 15 to 19 with an application surface for receiving the transfer layer (4), wherein the application surface has a surface tension of at least 0.6 mN per cm (60 dynes per cm). 21. A container (59) according to any one of claims 16 to 20, wherein the label (1) on the container (59) has a pin hardness between 1N and 7N in its dry state and a pin hardness less than 0.5N after a soaking time between 1 and 15 minutes in water as a soaking solution at 20 ⁰ C. 22. Container (59) according to one of claims 16 to 20, wherein the label (1) on the container (59) has a water absorption capacity after 3 hours of greater than 0 and less than 100 g/m ² , preferably around 5 g/m ² .