Method for labelling plastic containers

Abstract

The invention relates to a method for labelling plastic containers, which are made at least substantially of PP, PET or HDPE, wherein a PP film fastened to a support is printed, the label shapes are punched and separated from the support by way of a 180° deflection of the support and are glued to plastic containers being guided past. According to the invention, PP films, preferably BOPP films, are used for the labels, the modulus of elasticity of said films being at least ≥ 1300 MN / m2 and / or the tensile strength thereof being at least 150 MN / m2, preferably ≥ 170 MN / m2, both measured in the MD machine direction via ASTM D882.

Description

[0001] Procedure for labeling plastic containers

[0002] The invention relates to a method for labelling plastic containers which consist at least substantially of PP, PET or HDPE, wherein a PP film attached to a carrier is printed, the label shapes are punched and detached from the carrier by a 180° deflection of the latter and are glued onto passing plastic containers.

[0003] The advantage of using labels over printing on plastic containers is that, in a later recycling process, the label can be separated from the plastic container if different materials are selected for the label and the plastic container. This allows high-purity plastic to be recycled without the printing ink causing contamination. In addition to paper labels, which are generally less scratch- and impact-resistant, plastic labels, particularly those made of PP, have become established. These labels are attached to the plastic container using an adhesive. In a common process, a layer of the backing material for the label is provided with a layer of pressure-sensitive adhesive, which is then covered with a release liner or carrier.This release liner or carrier protects the adhesive during shipping and storage and allows for efficient handling of an array of individual labels after the label forms have been punched out and the matrix has been peeled from the facestock layer, up to the point where the individual label forms are sequentially dispensed onto a labeling machine. From punching out to dispensing, the release liner or carrier remains unpunched and can be rolled or unrolled for storage, delivery, and use of the array of dispensed individual label forms, or used unrolled as stackable goods.

[0004] To reduce costs, there is an urgent need for inexpensive films, with PE and PP films, the latter particularly as biaxially oriented polypropylene, having become the preferred choice. Another cost-saving measure was the suggestion to use PP films with a minimum thickness of 50 μm. Such films possess sufficient rigidity for dispensing under "normal conditions." However, difficulties arise when aesthetic designs are chosen for optical reasons, in which the label has irregular shapes rather than straight edges. If the reliable dispensing of the label from the carrier using a peel-off plate fails, the label or the label shape cannot be transferred to the plastic bottle without creases.In individual cases, one or more label shapes even jam, so that the entire labeling system must be shut down until the jammed and folded labels have been removed, after which the transfer process can be restarted.

[0005] Particular problems arise during the summer months, when outside temperatures exceed 40°C, especially in southern countries. If label films attached to a carrier are exposed to such high temperatures during transport, storage, or transfer, the label films lose the necessary rigidity, which complicates or hinders transfer and crease-free application. This effect occurs especially when existing air conditioning systems are turned off or their performance reduced to save energy.

[0006] It is therefore an object of the present invention to provide a method in which the label shapes are transferred onto the plastic container after punching, particularly in the case of irregular punching contours, in a secure and wrinkle-free manner.

[0007] This object is achieved by a method according to claim 1, in which the PP film is selected during labelling such that its modulus of elasticity is at least > 1300 MN / m 2 and / or whose tensile strength is at least 150 MN / m 2 , preferably > 170 MN / m 2 , both measured in MD machine direction via ASTM D882.

[0008] ASTM D882 is a standard method for determining the tensile properties of thin plastic films. Unlike the previously known state of the art, in which a uniform PP film thickness was used, disregarding temperature effects, the present invention always selects the specified value of the elastic modulus and / or tensile strength. This allows for possible PP film material softening, e.g., at temperatures > 40°C, to be taken into account by selecting a greater PP film thickness that meets the specified criteria. Excessive stiffness of the PP film, which is also a hindrance, is eliminated by limiting the specified minimum values ​​for the elastic modulus by a maximum of 300 MN / m. 2 and / or the tensile strength is maximum 220 MN / m 2be limited. Before the machine starts labeling, the ambient temperature or the material temperature of the label film attached to the carrier is determined, and the label film thickness is selected accordingly, which lies within the desired range of elastic modulus and / or tensile strength; both values ​​are indicators of sufficient minimum stiffness. Considering sufficient and adequate stiffness also prevents wrinkling of the labels adhered to the plastic container. Adhesive leakage at the cut edges caused by excessive softening of the PP film material is also prevented by the adjusted stiffness of the PP film material.

[0009] Further developments of the invention are described in the subclaims.

[0010] The use of an acrylate adhesive, which is used to attach the PP film to the carrier, has proven particularly effective. At higher temperatures, this has the advantage that the adhesive only takes hold after the composite, consisting of the label and the plastic bottle, has cooled.

[0011] The preferred carrier is glassine with a density of 62 g / m 2 up to 90g / m 2 or a plastic film as release carrier with a thickness of 20 pm to 30 pm.

[0012] For sustainability reasons, the PP, PET, or PE plastic containers contain recycled plastic granules, preferably in an amount of 10 to 50% by weight. While the addition of plastic granules leads to different surface tensions in the plastic container, this is surprisingly compensated for by the improved rigidity of the PP label material and the adhesives.

[0013] According to a further embodiment of the invention, the PP label shapes are guided past a dispensing edge after punching, which is formed by two guide surfaces arranged at an acute angle, preferably of 20° to 30°, to each other. Dispensing edges are known in principle from the prior art, but the guide surfaces used previously were at a significantly larger angle to each other. However, the acute angle selected according to the invention proves to be particularly advantageous for separating the punched label shapes from the carrier.

[0014] Preferably, materials other than polypropylene are chosen for the plastic containers, so that due to the different densities after shredding labelled plastic bottles in a washing solution, separation options arise that allow the printed PP material to be separated from PE, PET or HDPE.

[0015] The invention is further explained using exemplary embodiments described below.

[0016] In a first embodiment, a biaxially oriented polypropylene (BOPP) film with thicknesses between 51 and 56 pm is attached to a 25 pm release liner using an acrylate adhesive. The PP film had a tensile strength of 170 MN / m. 2 and a modulus of elasticity of 1300 MN / m 2 , each measured in the MD direction. Even at temperatures > 40°C and high machine speeds, the label shapes could be die-cut to size, particularly without adhesive leakage at the cut edges, and could be easily removed and affixed to a PET container without creases.

[0017] In another embodiment, BOPP films with thicknesses of 52 pm and 60 pm were used, which have a tensile strength of 200 MN / m 2 and elastic moduli of 2400 MN / m 2, each measured in the MD direction. Despite different thicknesses, error-free label transfers to PE containers were achieved, demonstrating that the selection of BOPP films with the inventive minimum tensile strengths and / or minimum elastic moduli at different temperatures up to 50°C is the decisive, surprising selection criterion.

Claims

Claims 1. A method for labelling plastic containers which consist at least substantially of PP, PET or HDPE, wherein a PP film attached to a carrier is printed, the label shapes are punched and detached from the carrier by a 180° deflection of the latter and are stuck onto plastic containers which are passed by, characterized in that the PP film, preferably a BOPP film for the labels is selected such that its modulus of elasticity is at least > 1300 MN / m 2 and / or whose tensile strength is at least 150 MN / m 2 , preferably > 170 MN / m 2 , both measured in MD machine direction via ASTM D882.

2. Method according to claim 1, characterized in that the PP film is attached to the carrier by means of an acrylate adhesive.

3. A method according to claim 1 or 2, characterized in that the support is made of glassine with a density of 62 g / m 2 up to 90 g / m 2or a plastic film as a release carrier with a thickness of 20 pm to 30 pm.

4. Method according to one of claims 1 to 3, characterized in that the PP, PET or PE plastic container contains portions of recycled plastic granulate, preferably in an amount of 10% to 50% by weight.

5. Method according to one of claims 1 to 4, characterized in that the PP label shapes are guided past a dispensing edge after punching, which is formed by two guide surfaces arranged at an acute angle, preferably of 20° to 30°, to one another.

6. Method according to one of claims 1 to 5, characterized in that the label molds and the plastic containers consist of materials with different densities, in particular of PP on the one hand and PE or PET on the other.