WO2020058323A1

WO2020058323A1 - In-mold label

Info

Publication number: WO2020058323A1
Application number: PCT/EP2019/074989
Authority: WO
Inventors: Yvonne DÜPRE; Melanie WISNIEWSKI
Original assignee: Treofan Germany Gmbh & Co. Kg
Priority date: 2018-09-20
Filing date: 2019-09-18
Publication date: 2020-03-26
Also published as: DE102018007419A1

Abstract

The invention relates to an in-mold label from a multi-layer, biaxially oriented polypropylene film, comprising at least a vacuole-containing base layer and an outer cover layer and an inner cover layer and an outer intermediate layer, the outer intermediate layer containing platelet aluminum particles.

Description

In-mold label

The present invention relates to a label film for in-mold labeling (IML), and to a method for producing these label films and their use.

Label foils cover an extensive and technically complex area. A distinction is made between different labeling techniques, which are fundamentally different with regard to the process conditions and inevitably place different technical requirements on the label materials. All labeling processes have in common that the end result must be visually appealing labeled containers, in which good adhesion to the labeled container must be guaranteed.

In the labeling process, very different techniques are used to apply the label. A distinction is made between self-adhesive labels, wrap-around labels, shrink labels, in-mold labels, patch labeling, etc. The use of a film made of thermoplastic plastic as a label is possible in all of these different labeling methods.

A distinction is also made between in-mold labeling and different techniques, in which different process conditions are used. All in-mold labeling processes have in common that the label takes part in the actual shaping process of the container and is applied in the process. However, very different molding processes are used here, such as injection molding, blow molding and deep drawing.

In all in-mold labeling processes, individual labels are cut, stacked, removed from the stack and inserted into the respective shape. As a result, the separability (unstackability) of the labels is a critical factor for the efficiency of the entire labeling process.

EP 0 61 1 102 B1 discloses a biaxially oriented polypropylene film which has a vacuole-containing base layer made of polypropylene homopolymer with an intermediate layer made of vacuole-free polypropylene homopolymer on one Surface and a printable outer layer on the vacuole-free polypropylene-flomopolymer intermediate layer comprises. The printable outer layer is formed from a polyolefin copolymer which is composed of ethylene, propylene, but-1-ene and higher a-olefins units. In addition, there is at least one further polymer layer on the surface opposite the vacuole-free intermediate layer, the outer surface of which is matt and comprises a mixture of incompatible polymers. The inner layer and / or the vacuole-free layer further contains titanium dioxide. The film in this publication is used, among other things, for in-mold labeling.

In the field of packaging films, films are often metallized, for example to give the film barrier properties. In some applications, the foils are also metallized only with a view to the visual impression. Here the consumer should get the impression of high-quality packaging without actually having a better barrier. For these reasons, label films are also metallized in some applications so that the labels underline and reinforce the impression of a high-quality product. However, the metallization of foils for in-mold labels is problematic.

On the one hand, the additional metallization increases the cost of the label, since the metallization itself takes place in a separate processing step. In addition, the metal layer must be protected by lamination or a top coat. These processing steps such as metallization and lamination influence the flatness of the film, so that undesirable curling effects can occur when cutting labels.

When used as an in-mold label, the foils are cut, stacked, removed from the stack and inserted into the respective shape. Here, the film cuts must not bulge. In addition, a certain charge of the film is important for the positioning of the label in the mold in order to position and close the label in the mold using electrostatic forces hold. The loading of the film ensures that the label adheres well to the mold until the container is molded by flinter spraying the label and the label becomes an integral part of the container. The foils are quickly discharged via the metal layer so that the label can no longer be adequately fixed using electrostatic forces. Therefore, in-mold labels made of metallized foils are more often positioned poorly or incorrectly in the form, so that the containers are sorted out as optically defective.

It was an object of the present invention to provide a film which can advantageously be used as an in-mold label and which, even after application to the container, gives the impression of a metallized label and can be used without problems in the entire processing process, in particular one allows good fixation in the form and optically has a metallic appearance after labeling.

The other requirements with regard to use as an in-mold label must not be affected, i.e. the film must at the same time have good printability on its outside and the printed label must have good adhesion to the container, and as a single label it must have good stackability and unstackability and no curling.

This object is achieved by an in-mold label made from a multilayer, biaxially oriented polypropylene film which comprises at least one vacuole-containing base layer and an outer cover layer and an inner cover layer and an outer intermediate layer, the outer intermediate layer containing platelet-shaped aluminum particles.

The subclaims indicate preferred embodiments of the invention.

In the following, the inner surface or inner cover layer is the surface or cover layer of the label film that is in contact with the container after labeling. The outer surface or outer cover layer is accordingly the opposite surface or the opposite cover layer of the film which is printed and after the Labeling is visible. Accordingly, the inner intermediate layer between the base layer and the inner cover layer and the outer intermediate layer between the base layer and the outer cover layer is attached.

In the context of the present invention, it was found that the finishing of the intermediate layer according to the invention with platelet-shaped aluminum particles gives the label a characteristic metallic appearance and the disadvantages of the metallization are avoided. The label can be positioned very well in the mold and shows a shimmering silver-colored metallic look after the injection molding of the container, which results from the combination of the vacuole-containing base layer and the pigmented intermediate layer. Surprisingly, the metallic impression of the label is retained even after the label has come into contact with the hot melt. The result is a labeled container, in which the label is an integral part of the container and gives the impression of a high-quality metallized label. In the following, the intermediate layer, which according to the invention contains aluminum particles, is referred to as “pigmented intermediate layer”

The other properties for using the film as an in-mold label are also not impaired. The film can be easily printed with a wide variety of colors on the outer surface and the printed label can also be stacked and separated easily, the label shows no tendency to curl and the flow against the container is not impaired. As a result, a film is made available which can be processed to the label at very high speeds and which in the end leads to a perfectly labeled container with a high-quality label.

The pigmented intermediate layer gives both glossy foils and matt designs the desired metallic look. Shiny embodiments have a thin cover layer made of propylene copolymers, propylene terpolymers and / or propylene homopolymers on the pigmented intermediate layer, the gloss emphasizing the metallic appearance of the surface. Surprisingly, the gloss is due to the pigmentation of the outer Intermediate layer less lowered than with pigmentation of the top layer.

In a matt embodiment, the outer cover layer is constructed from a mixture of incompatible polymers known per se which has a lower gloss. Here, the combination with the pigmented intermediate layer leads to a special look, which emphasizes the orange-peel effect of the labels and shows a matt metallic appearance.

In a preferred embodiment, the label film is a five-layer film which has at least one intermediate layer on both surfaces of the base layer. The printable outer cover layer is applied to the outer intermediate layer and the inner cover layer is applied to the opposite inner intermediate layer.

The base layer of the film generally contains at least 70% by weight, preferably 75 to 99% by weight, in particular 80 to 98% by weight, in each case based on the weight of the base layer, propylene polymers and at most 30% by weight, preferably 1 to 25% by weight .-%, in particular 2 to 20 wt .-%, particularly preferably 5 to 15 wt .-% vacuole-initiating fillers, and optionally further conventional additives in effective amounts in each case. Preferred embodiments do not contain pigments, i.e. <1% by weight, in particular no T1O2, in the base layer.

In general, the propylene polymer contains at least 90% by weight, preferably 94 to 100% by weight, in particular 98 to <100% by weight, of polypropylene units. The corresponding comonomer content of at most 10% by weight or 0 to 6% by weight or> 0 to 2% by weight is, if present, generally derived from ethylene. The percentages by weight relate to the propylene polymer.

Isotactic propylene homopolymers with a melting point of 140 to 170 ° C., preferably 150 to 165 ° C., and a melt flow index (measurement ISO 1 133 at 2.16 kg load and 230 ° C.) of 1.0 to 10 g / 10 are preferred min, preferably from 1.5 to 6.5 g / 10 min. The n-heptane soluble portion of the polymer is generally 0.5 to 10% by weight, preferably 2 to 5% by weight, based on the starting polymer. The molecular weight distribution of the propylene polymer can vary. The ratio of the weight average Mw to the number average Mn is generally between 1 and 15, preferably between 2 and 10, very particularly preferably between 2 and 6. Such a narrow molecular weight distribution of the propylene polymer of the base layer can be achieved, for example, by its peroxidic degradation or by the preparation of the polypropylene using suitable metallocene catalysts. Highly isotactic or highly crystalline polypropylenes are also suitable for the purposes of the present invention, the isotacticity of which, according to ¹³ C-NMR (triad), is at least 95%, preferably 96-99%. Such highly isotactic polypropylenes are known per se in the prior art and are referred to both as HIPP and as HCPP.

For the purposes of the present invention, “pigments” are incompatible particles which essentially do not lead to the formation of vacuoles when the film is stretched. The coloring effect of the pigments is caused by the particles themselves. Pigments generally have an average particle diameter of 0.01 to at most 1 miti, preferably 0.01 to 0.7 miti, in particular 0.01 to 0.4 miti. Pigments include both so-called "white pigments", which color the film white, as well as "colored pigments", which give the film a colorful or black color. Of course, pigments in the context of the present invention do not include the aluminum particles added according to the invention.

For the purposes of the present invention, “vacuole-initiating fillers” are solid particles which are incompatible with the polymer matrix and lead to the formation of vacuole-like cavities when the films are stretched, the size, type and number of vacuoles depending on the size and amount of the solid particles and the stretching conditions, such as stretching ratio and stretching temperature. The vacuoles reduce the density and give the films a characteristic pearlescent, opaque appearance, which is caused by light scattering at the "vacuole / polymer matrix" interfaces. The light scattering on the solid particles themselves generally contributes comparatively little to the opacity of the film. As a rule, the vacuole-initiating fillers have a minimum size of 1 miti in order to lead to an effective, ie opaque, amount of vacuoles. In general, the average particle diameter of the particles is 1 to 6 miti, preferably 1, 5 to 5 miti. The chemical character of the particles plays a minor role if there is an incompatibility.

Usual vacuole-initiating fillers are inorganic and / or organic materials incompatible with polypropylene, such as aluminum sulfate, barium sulfate, calcium carbonate, magnesium carbonate, silicates, such as aluminum silicate (kaolin clay) and magnesium silicate (talc) and silicon dioxide, of which calcium carbonate and silicon dioxide are preferably used. Suitable organic fillers are the commonly used polymers which are incompatible with the polymer of the base layer, in particular those such as FIDPE, copolymers of cyclic olefins such as norbornene or tetracyclododecene, with ethylene or propylene, polyester, polystyrenes, polyamides, halogenated organic polymers, where Polyesters such as polybutylene terephthalates are preferred. For the purposes of the present invention, “incompatible materials” or “incompatible polymers” refer to those materials or polymers which are present in the film as separate particles or as a separate phase.

The density of the film according to the invention can vary within a wide range depending on the composition of the base layer. Vacuoles contribute to lowering the density. The density of the film is preferably in the range from 0.4 to 0.8 g / cm ³ , in particular in the range from 0.5 to 0.75 g / cm ³ .

In addition, the base layer can contain conventional additives, such as neutralizing agents, stabilizers, antistatic agents and / or further lubricants, in each case in effective amounts. The following percentages by weight relate to the weight of the base layer.

Preferred antistatic agents are glycerol monostearates, alkali alkanesulfonates, polyether-modified, in particular ethoxylated and / or propoxylated, polydiorganosiloxanes (polydialkylsiloxanes, polyalkylphenylsiloxanes and the like) and / or the essentially straight-chain and saturated aliphatic, tertiary amines with an aliphatic having 20 to 20 aliphatic atoms -Flydroxy- (Ci-C ₄ ) alkyl groups are substituted, where N, N-bis (2-hydroxyethyl) alkylamines with 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, are particularly suitable in the alkyl radical. The preferred amount of antistatic is in the range of 0.05 to 0.5% by weight.

Higher aliphatic acid amides, higher aliphatic acid esters, waxes and metal soaps are particularly suitable as lubricants. The preferred amount of lubricant is in the range of 0.01 to 3% by weight, preferably 0.02 to 1% by weight. The addition of higher aliphatic acid amides in the range from 0.01 to 0.25% by weight in the base layer is particularly suitable. Very particularly suitable aliphatic acid amides are erucic acid amide and stearylamide.

The usual stabilizing compounds for ethylene, propylene and other olefin polymers can be used as stabilizers. The amount added is preferably between 0.05 and 2% by weight. Phenolic and phosphitic stabilizers, such as tris-2,6-dimethylphenyl phosphite, are particularly suitable. Phenolic stabilizers with a molecular weight of more than 500 g / mol are preferred, in particular pentaerythrityl tetrakis 3- (3,5-di-tertiary-butyl-4-hydroxyphenyl) propionate or 1,3,5-trimethyl-2, 4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene. Phenolic stabilizers alone are advantageously used in an amount of 0.1 to 0.6% by weight, in particular 0.1 to 0.3% by weight, phenolic and phosphitic stabilizers preferably in a ratio of 1: 4 to 2: 1 and in a total amount of 0.1 to 0.4 wt .-%, in particular 0.1 to 0.25 wt .-%, used.

Preferred neutralizing agents include dihydrotalcite, calcium stearate and / or calcium carbonate with an average particle size of at most 0.7 miti, an absolute particle size of less than 10 pm and a specific surface area of at least 40 m ² / g. Generally 0.02 to 0.1% by weight is added.

The film according to the invention comprises at least one inner cover layer and one outer cover layer. For the purposes of the present invention, the inner cover layer is that cover layer which faces the container during labeling and forms the connection between the container and the label. The inner cover layer is either in contact with the base layer or preferably in contact with the inner intermediate layer. The outer cover layer in the sense of the present invention is that cover layer which faces away from the container during labeling and points outwards during labeling and is visible on the labeled container. The outer cover layer is in contact with the outer intermediate layer.

The inner cover layer generally has a thickness of 0.5 to 5miti, preferably 0.8 to 3miti. The outer cover layer (without aluminum particles) generally has a thickness of 0.5 to 5 miti, preferably 0.5 to 3 miti. The optional inner intermediate layer generally has a thickness of 1.5 to qmiti, preferably 2 to 4.5miti. The outer intermediate layer generally has a thickness of greater than 1 miti and is preferably in the range from 1.5 to 15 miti, in particular from 2 to 10 miti, for example from 2.5 to 8 pm or from 3 to 6 miti.

The total thickness of the film is preferably in a range from 30 to 10 μm, preferably in a range from 40 to 80 μm. The base layer is generally the thickest layer of the film and preferably makes up 40 to 99% of the total film thickness. The film can optionally have further layers.

The label film preferably has a matt inner cover layer which contains at least two incompatible polymers (A) and (B) as essential components. For the purposes of the present invention, incompatible means that the two polymers form two separate phases and thereby produce an increased roughness of the surface. Such matt cover layers made of incompatible polymers are known per se in the prior art.

In general, the cover layer is built up from (A) propylene homopolymer, co- and / or terpolymer from propylene, ethylene and / or butylene units and (B) polyethylene. In general, the inner cover layer contains at least 30 to 95% by weight, preferably 45 to 85% by weight, in particular 50 to 80% by weight of the propylene polymers (A) mentioned and 5 to 70% by weight, preferably 15 to 55% by weight, in particular 20 to 50% by weight, of the polyethylene (B), in each case based on the weight of the inner cover layer. Propylene copolymers or propylene terpolymers which are particularly suitable for the present purposes contain predominantly propylene units and additionally ethylene units and / or butylene units, ie in particular propylene-ethylene copolymers, propylene-butylene copolymers or propylene-ethylene-butylene terpolymers. The composition of the propylene copolymers or propylene terpolymers from the respective monomers can vary within the limits described below. In general, the propylene polymers contain more than 50% by weight of polypropylene units, which is why they are also referred to as propylene copolymers. Preferred propylene copolymers contain at least 60% by weight, preferably 65 to 97% by weight, of polypropylene units and at most 40% by weight, preferably 3 to 35% by weight, of ethylene or polybutylene comonomer units. Terpolymers which contain 65 to 96% by weight, preferably 72 to 93% by weight of polypropylene units, and 3 to 34% by weight, preferably 5 to 26% by weight of polyethylene units and 1 up to 10 wt .-%, preferably 2 to 8 wt .-% polybutylene units.

The melt index of the propylene copolymers or propylene terpolymers is generally 0.1 to 20 g / 10 min (230 ° C., 2.16 kg), preferably 0.1 to 15 g / 10 min. The melting point can generally range from 70 to 140 ° C. In a preferred embodiment, propylene copolymers and / or propylene terpolymers are used, the melting point of which is at least 105 to 140 ° C., preferably 1 10 to 135 ° C.

Suitable propylene homopolymers are those which have already been described above for the base layer and can also be added to the inner cover layer, the proportion of propylene homopolymer generally not being> 50% by weight, based on the weight of the inner cover layer.

The propylene polymers mentioned above can optionally be mixed with one another. The proportions can be varied within any limits. These mixtures are then used in the cover layer in the amounts described above for the propylene polymers. The second essential component of the matt inner cover layer is at least one polyethylene which is incompatible with the propylene polymers described above. Such incompatible mixtures of propylene polymers and polyethylenes are known per se in the prior art. The mixtures of the propylene polymers and the incompatible polyethylenes produce a surface roughness which basically gives the surface of the inner cover layer a matt appearance. "Incompatible" in the sense of this invention therefore means that a surface roughness is formed by the mixture of the propylene polymer and the polyethylene.

Suitable incompatible polyethylenes are, for example, HDPE or MDPE. The HDPE generally has the properties described below, for example an MFI (21.6 kg / 190 ° C.) of greater than 1 to 50 g / 10 min, preferably 1.5 to 30 g / 10 min, measured in accordance with ISO 1 133 and a viscosity number, measured according to DIN 53 728, part 4, or ISO 1 191, in the range from 100 to 450 cm ³ / g, preferably 120 to 280 cm ³ / g. The crystallinity is generally 35 to 80%, preferably 50 to 80%. The density, measured at 23 ° C. according to DIN 53 479, method A, or ISO 1183, is preferably in the range from> 0.94 to 0.96 g / cm ³ . The melting point, measured with DSC (maximum of the melting curve, heating rate 20 ° C./min), is preferably between 120 and 140 ° C. Suitable MDPE generally has an MFI (21.6 kg / 190 ° C.) of greater than 0.1 to 50 g / 10 min, preferably 0.6 to 20 g / 10 min, measured according to ISO 1 133. The density, measured at 23 ° C according to DIN 53 479, method A, or ISO 1 183, is preferably in the range from> 0.925 to 0.94 g / cm ³ . The melting point, measured with DSC (maximum of the melting curve, heating rate 20 ° C./min), is preferably between 115 and 135 ° C., preferably 115 to 130 ° C.

If necessary, the inner cover layer can contain small amounts of further olefinic polymers, provided that this does not impair the essential film properties. The surface of the inner cover layer is optionally subjected to a corona or flame treatment. If appropriate, the inner cover layer can contain conventional additives in effective amounts in each case, and further polymers in small amounts (0 to <5% by weight), provided that these additives do not impair the properties of the film which are essential to the invention.

These are, for example, the additives described in part above, such as neutralizing agents, stabilizers, antistatic agents and / or antiblocking agents. The respective details in% by weight relate to the weight of the inner cover layer.

Particularly suitable antiblocking agents are inorganic additives, such as silicon dioxide, calcium carbonate, magnesium silicate, aluminum silicate, calcium phosphate and the like and / or incompatible organic polymers, such as polyamides, polyesters, polycarbonates and the like, or crosslinked polymers, such as crosslinked polymethyl methacrylate or crosslinked silicone oils. Silicon dioxide and calcium carbonate are preferred. The average particle size is preferably between 1 and 6%, in particular 2 and 5%. The preferred amount of antiblocking agent is in the range from 0.05 to 5% by weight, preferably 0.1 to 3% by weight, in particular 0.2 to 2% by weight.

The polyolefin film according to the invention has a second, outer cover layer on the side opposite the inner cover layer. The outer cover layer should have a good flow compared to conventional printing inks. This outer cover layer is applied to the surface of the outer intermediate layer. A corona, plasma or flame treatment is preferably carried out on the surface of the outer cover layer to further improve the printability.

The outer cover layer is generally composed of polymers from olefins having 2 to 10 carbon atoms. The outer cover layer generally contains 95 to 100% by weight of polyolefin, preferably 98 to <100% by weight of polyolefin, in each case based on the weight of the cover layer / s. For embodiments with a higher gloss on the outer surface, propylene homopolymers, propylene copolymers or propylene terpolymers II composed of ethylene, propylene and / or butylene units or mixtures of the polymers mentioned are preferred. They are polyolefins. Preferred polymers include statistical ethylene-propylene copolymers with an ethylene content of 1 to 10% by weight, preferably 2.5 to 8% by weight, or statistical propylene-butylene-1 copolymers with a butylene content of 2 to 25% by weight %, preferably 4 to 20% by weight, or statistical ethylene-propylene-butylene-1 terpolymers with an ethylene content of 1 to 10% by weight and a butylene-1 content of 2 to 20% by weight , or a mixture or a blend of ethylene-propylene-butylene-1 terpolymer and propylene-butylene-1 copolymers with an ethylene content of 0.1 to 7% by weight and a propylene content of 50 to 90% by weight % and a butylene-1 content of 10 to 40 wt .-%. The percentages by weight relate to the weight of the polymer.

The above-described propylene copolymers and / or propylene terpolymers II used in the outer cover layer generally have a melt flow index of 1.5 to 30 g / 10 min, preferably 3 to 15 g / 10 min. The melting point is in the range from 120 to 145 ° C. The blend of copolymers and terpolymers II described above has a melt flow index of 5 to 9 g / 10 min and a melting point of 120 to 150 ° C. All melt flow indices given above are measured at 230 ° C and a force of 21.6 N (DIN 53 735).

These embodiments described above with co- or terpolymer cover layers show a gloss of 40 to 80 gloss units (GU), preferably 50 to 75 GU, each at an angle of 60 ° on the outer surface.

Suitable propylene homopolymers for the outer cover layer are the propylene homopolymers described above for the base layer.

These embodiments described above with a propylene homopolymer top layer have a gloss of 60 to 130 gloss units (GU), preferably 80 to 120 GU, in each case at an angle on the outer surface of 60 °, or a gloss of 40 to 80 gloss units (GU), preferably 50 to 75 GU, each at an angle of 20 °.

In a further matt embodiment, the outer cover layer can additionally contain an incompatible polymer analogously to that described for the inner cover layer and thus have a matt and rough surface.

This matt outer cover layer is composed of the propylene homopolymers or copolymers and / or terpolymers of propylene, ethylene and / or butylene units (A) and polyethylene (B) described above. In general, the matt outer cover layer contains at least 30 to 95% by weight, preferably 45 to 85% by weight, in particular 50 to 80% by weight of the propylene polymers (A) mentioned and 5 to 70% by weight, preferably 15 up to 55% by weight, in particular 20 to 50% by weight, of the polyethylene (B), in each case based on the weight of the outer cover layer.

Suitable incompatible polyethylenes are described in detail in connection with the inner cover layer. These polyethylenes are equally suitable for the matt outer cover layer.

The same applies to the matt outer cover layer that the mixture of the propylene polymers and the incompatible polyethylenes creates a surface roughness that gives the surface of the outer cover layer a matt appearance and a low gloss. These described embodiments with a matt cover layer of incompatible polymers show a gloss of 5 to <40 gloss units (GU), preferably 10 to 30 GU, in each case at an angle of 60 ° on the outer surface.

Optionally, the additives described above, such as antistatic agents, neutralizing agents, antiblocking agents and / or stabilizers, can be added to the outer cover layer, both in the matt and in the glossy embodiment. The data in% by weight then relate accordingly to the weight of the cover layer. Suitable antiblocking agents have already been described in connection with the inner cover layer. These antiblocking agents are also suitable for the outer cover layer. The preferred amount of antiblocking agent for the outer cover layer is in the range from 0.1 to 2% by weight, preferably 0.1 to 0.8% by weight.

In a particularly preferred embodiment, the surface of the outer cover layer is treated with corona, plasma or flame. This treatment improves the adhesive properties of the film surface for subsequent decoration and printing, i.e. to ensure the wettability and adhesion of printing inks.

The film according to the invention comprises an outer intermediate layer, which is arranged between the base layer and the outer cover layer, and optionally an inner intermediate layer, which is arranged between the base layer and the inner cover layer. The outer intermediate layer is in contact with the outer cover layer, the inner intermediate layer is in contact with the inner cover layer. Preferred embodiments of the film have five layers and have an inner and an outer intermediate layer.

The inner intermediate layer and the outer intermediate layer each independently contain at least one polymer of at least one olefin, preferably at least one propylene polymer, in particular at least one propylene homopolymer. Furthermore, the inner intermediate layer and the outer intermediate layer can each independently of one another contain the customary additives described for the individual layers, such as antistatic agents, neutralizing agents, lubricants and / or stabilizers, and, if appropriate, pigments.

Preferred polymers of the intermediate layers are isotactic propylene homopolymers with a melting point of 140 to 170 ° C, preferably from 150 to 165 ° C, and a melt flow index (measurement ISO 1 133 at 2.16 kg load and 230 ° C) from 1.0 to 10 g / 10 min, preferably from 1.5 to 6.5 g / 10 min. The n-heptane-soluble fraction of the polymer is generally 0.5 to 10% by weight, preferably 2 to 5% by weight, based on the starting polymer. For the purposes of the present invention, the above are for the base layer The highly isotactic or highly crystalline polypropylenes described can be used in the intermediate layers and are advantageous, for example, for films with a thickness of less than 60 pm, preferably from 35 to 55, in particular from 40 to 50 pm. If necessary, the use of highly crystalline polypropylenes in the intermediate layers can improve the rigidity of films with a particularly low density of the base layer.

Alternatively, the intermediate layers can also be propylene homopolymers with a regular isotacticity ( ¹³ C-NMR) of 90 to 96%, preferably 92 to <95%, in particular for films with a thickness of> 60 to 100 pm.

The intermediate layer each contains 90-100% by weight of the propylene polymers described, preferably propylene homopolymers, and, if appropriate, additionally the additives mentioned. In addition, the inner intermediate layer and the outer intermediate layer, in particular the outer intermediate layer, can contain pigments, in particular TiO 2, for example in an amount of 2 to 8% by weight, the proportion of polymer being reduced accordingly. In the context of the present invention, however, films without T1O2 are preferred.

The thickness of the pigmented outer intermediate layer is generally greater than 1 μm and is preferably in the range from 1.5 to 15 μm, in particular from 2 to 10 μm, for example from 2.5 to 8 μm or from 3 to 6 μm.

According to the invention, the outer intermediate layer contains 2 to 30% by weight, in particular 3.5 to 25% by weight, based on the weight of the intermediate layer, of flake or scale-shaped aluminum particles. Platelet-shaped aluminum particles are characterized by a non-spherical shape. They are very thin in one dimension and comparable to dandruff. For example, the flakes can resemble the shape of "cornflakes" and then show broken edges that result from the grinding process. The aluminum particles preferably have rounded edges and a shape which is referred to as the silver dollar. The ratio of length or width (largest dimension) to thickness (smallest dimension) of the platelets is generally referred to as “aspect ratio” and is generally in a range from 50: 1 to 1000: 1, with higher aspect Ratios of 100: 1 to 500: 1 are preferred. The thickness of the platelets is generally less than <2miti and is preferably in a range from 0.05 to 0.9miti. The length or width of the platelets should not exceed 100miti and is generally in the range of 1 to dqmiti.

Such aluminum pigments are known per se and are sold, for example, by the Altana company.

Because of the preferred composition of the layers of propylene polymers, the film is referred to as polypropylene film. For the purposes of the present invention, this means that the film has a proportion of at least 70% propylene units, preferably 90 to 98% propylene units, based on the film.

In a further, non-preferred embodiment, the film can additionally or alternatively contain the aluminum pigments in the outer cover layer. These embodiments also have the desired metallic look, but the abrasion caused by the aluminum particles puts a strain on the systems for producing the film. It has been found within the scope of the invention that, surprisingly, a high layer thickness of the pigmented outer cover layer reduces the abrasion, although the pigments are generally uniformly distributed in the layer.

In these embodiments, the outer cover layer therefore has a thickness of 3 to 7 pm, preferably 4 to 6 pm, in order to ensure good embedding of the particles in the polymer and thus to counteract the disadvantageous abrasion by the particles. The aluminum pigments are contained in the top layer in comparable amounts as in the intermediate layer. The outer cover layer thus contains 2 to 30% by weight, in particular 3.5 to 25% by weight, based on the weight of the cover layer of the platelet-shaped or scale-shaped aluminum particles, which are described above in connection with the outer intermediate layer are described. In a further embodiment, the pigmented outer cover layer can be combined with the pigmented outer intermediate layer described. The film according to the invention can be produced in a manner known per se, for example by a coextrusion process. As part of this process, the melts corresponding to the individual layers of the film are co-extruded simultaneously and together through a flat die, the film thus obtained is drawn off for consolidation on one or more rollers, the multilayer film is then stretched (oriented), the stretched film is heat-set and subjected to a corona treatment on the inner surface, and optionally plasma, corona or flame treated on the outer surfaces.

Biaxial stretching (orientation) can be carried out sequentially or simultaneously. Sequential stretching is generally carried out sequentially, with sequential biaxial stretching, in which stretching first lengthwise (in the machine direction) and then transversely (perpendicular to the machine direction) is preferred. The further description of the film production is based on the example of the preferred flat film extrusion with subsequent sequential stretching.

First, as is customary in the extrusion process, the polymer or the polymer mixture of the individual layers is compressed and liquefied in an extruder, and the additives which may have been added may already be present in the polymer or in the polymer mixture. The melts are then extruded together and simultaneously through a flat die (slot die) and the multilayer melt is drawn off on one or more take-off rolls, preferably at a temperature of 10 to 100 ° C., in particular 10 to 50 ° C., where it cools and solidifies .

The undrawn pre-film thus obtained is then generally stretched longitudinally and transversely to the direction of extrusion, which leads to an orientation of the molecular chains. The longitudinal stretching is preferably carried out at a temperature of 70 to 130.degree. C., in particular 80 to 110.degree. C., expediently with the aid of two rollers running at different speeds in accordance with the desired stretching ratio, and the transverse stretching preferably at a temperature of 120 to 180 ° C with the help of an appropriate tenter frame. The longitudinal stretching ratios are advantageously in the range from 3 to 8, preferably 4 to 6. The transverse stretching ratios are advantageously in the range from 5 to 10, preferably 7 to 9.

The stretching of the film is preferably followed by its heat setting (heat treatment), the film advantageously being kept at a temperature of 100 to 160 ° C. for about 0.1 to 10 s. The film is then wound up in a conventional manner using a winding device.

After the biaxial stretching, the inner surface of the film is corona-treated, preferably the outer surface is also plasma, corona or flame-treated by one of the known methods. The treatment intensity for both surfaces, independently of one another, is generally in the range from 35 to 50 mN / m, preferably 37 to 45 mN / m.

The corona treatment is expediently carried out in such a way that the film is passed between two conductor elements serving as electrodes, such a high voltage, usually alternating voltage (approximately 5 to 20 kV and 5 to 30 kHz) being applied between the electrodes that spray or corona discharges can take place. As a result of the spray or corona discharge, the air above the film surface is ionized and reacts with the molecules of the film surface, so that polar deposits occur in the essentially non-polar polymer matrix.

Processes for flame treatment are also known per se and are described, for example, in EP 0732 188. The treatment intensity is generally in the range from 37 to 50 mN / m, preferably 39 to 45 mN / m. In general, this flame treatment is carried out using a flame without polarization. If necessary, polarized flames can also be used. The film is passed over a cooling roller during the flame treatment, a burner being attached above this roller. This burner is generally placed at a distance of 3 to 10mm from the film surface / chill roll. During contact with the flame, the film surface undergoes an oxidation reaction. The film is preferably cooled via the cooling roll during the treatment. The roller temperature is in the range of 15 to 65 ° C, preferably 20 to 50 ° C.

The films according to the invention can be printed, for example, using the sheet-fed printing process or an alternative printing process. After printing, the individual labels are cut or punched and stacked into a stack of individual printed labels. The labels can be used in all common in-mold labeling processes. The film according to the invention is particularly suitable as an in-mold label in the injection molding process. In this use, the film is applied during the molding process of the container and becomes an integral part of the molded container. The containers are generally made from suitable propylene or ethylene polymers, i.e. sprayed.

In the injection molding process, the individual, possibly cut, labels are first removed from a stack so that they can be inserted into an injection mold. The shape is designed in such a way that the melt flow of the polymer is injected behind the label and the front of the film lies against the wall of the injection mold. When spraying, the hot melt combines with the label. After spraying, the tool opens, the molded part with the label is ejected and cools down. As a result, a labeled container is produced, on which the label adheres wrinkle-free and optically perfect on the container.

When spraying, the injection pressure is preferably in a range from 300 to 600 bar. The plastics used, in particular propylene polymers or polyethylenes, advantageously have a melt flow index of around 40 g / 10 min. The injection temperatures depend on the plastic used. In some cases, the mold is additionally cooled and the molding is prevented from sticking to the mold.

In the following, the present invention is further illustrated by examples and comparative examples, without any intention that this should limit the inventive concept. The following measurement methods were used to characterize the raw materials and the foils:

Melt flow index

The melt flow index of the propylene polymers was measured according to ISO 1 133 at 2.16 kg load and 230 ° C. and at 190 ° C. and 21.6 kg for polyethylenes.

Melting points

The melting point is determined in accordance with DIN 51007 as the maximum of the melting curve from a DSC measurement, the melting curve being recorded at a heating rate of 20 K / min.

density

The density of the polymers is determined in accordance with DIN 53 479, method A. The density of the foils is calculated from the measured thickness and the measured basis weight (ISO 4593).

Surface tension

The surface tension was determined using the ink method according to DIN ISO 8296.

Gloss measurement

The measurement was carried out in accordance with DIN EN ISO 2813 at an angle of 20 ° and 60 °. The standard used was a polished, dark-colored glass plate with a refractive index of 1,567 (measured at a wavelength of 587.6 nm and 25 ° C.), the gloss of which corresponds to 100 gloss units.

CIE = L ^* a ^* b ^*

The color measurement was carried out in accordance with DIN 5033. The sample was irradiated with the light source D65 and the geometry 45 ° a: 0 °. The observation angle in this measurement was 10 °.

Static charging and discharging The measurement was carried out in accordance with DIN EN 613 40-2-1. The maximum field strength and its percentage reduction after 3 seconds were determined.

The invention is illustrated below by the following examples.

example 1

A five-layer prefilm was extruded from a slot die using the coextrusion process. This pre-film was removed on a chill roll, solidified and then oriented in the longitudinal and transverse directions and finally fixed. The surface of the outer and inner cover layers was pretreated with corona. The five-layer film had a layer structure of inner cover layer / inner intermediate layer / base layer / outer intermediate layer / outer cover layer. The individual layers of the film had the following composition:

inner cover layer I (2.3 pm):

~ 64.8 wt .-% ethylene-propylene copolymer with a melting point of

135 ° C and a melt flow index of 7.3 g / 10 min at 230 ° C and 2.16 kg load (ISO 1133)

- 35.0% by weight MDPE with an MFI of 14.4 g / 10min (21.6 kg and 190 ° C);

Density of 0.937g / ccm3 and a melting point of 126 ° C

0.12% by weight of SiO 2 as an antiblocking agent

inner intermediate layer I (3.0 pm)

100 wt .-% propylene homopolymer with an n-heptane soluble content of

4.5% by weight (based on 100% PP), a melting point of 165 ° C and a melt flow index of 3.2 g / 10 min at 230 ° C and 2.16 kg load (ISO 1133)

Base layer (49.6 pm)

86.8 wt .-% propylene homopolymer (PP) with an n-heptane-soluble

Proportion of 4.5% by weight (based on 100% PP) and a melting point of 165 ° C and a melt flow index of 3.2 g / 10 min at 230 ° C and 2.16 kg load (ISO 1133)

-13% by weight calcium carbonate with an average particle diameter of

3.5 pm 0.1% by weight erucic acid amide (ESA)

0.1% by weight Armostat 300

outer intermediate layer II (3.4 mhh)

100% by weight propylene homopolymer (PP) with an n-heptane soluble

Proportion of 4.5% by weight (based on 100% PP), a melting point of 165 ° C and a melt flow index of 3.2 g / 10 min at 230 ° C and 2.16 kg load (ISO 1133)

outer cover layer II (4.7 pm):

95.2 wt .-% propylene homopolymer (PP) with an n-heptane-soluble

4.8 wt .-% platelet-shaped aluminum particles with a medium

Particle size of 11 pm

All layers of the film additionally contained stabilizer and neutralizing agent in the usual amounts.

The following conditions and temperatures were selected for the production of the film:

Extrusion: extrusion temperature approx. 250 ° C

Cooling roller: temperature 27 ° C

Longitudinal stretch: T = 100 ° C

Longitudinal stretching by a factor of 5.3

Lateral stretch: T = 150 ° C

Lateral stretching by a factor of 8

Fixation T = 140 ° C

The film was surface treated with Corona on both surfaces. The film had a metallic appearance and a density of 0.55 g / cm ³ and a thickness of 63 μm. Example 2

A film was produced according to Example 1, in contrast to Example 1, the homopolymer in the outer cover layer II was replaced by a propylene copolymer. The composition of the outer cover layer was therefore as follows:

outer cover layer II (4.7 miti):

95.2% by weight of ethylene-propylene copolymer with a melting point of

4.8 wt .-% platelet-shaped aluminum particles with a medium

Particle size of 11 pm

The thickness of the layers, as well as the composition of all other layers, and the conditions during the production of the film remained unchanged.

Example 3

A film was produced as described in Example 1. In contrast to Example 1, the platelet-shaped aluminum was not incorporated into the outer cover layer, but only into the outer intermediate layer. The composition of the outer cover layer and the outer intermediate layer was therefore the following:

outer intermediate layer II (3.2 pm)

95.2 wt .-% propylene homopolymer (PP) with an n-heptane-soluble

4.8 wt .-% platelet-shaped aluminum particles with a medium

Particle size of 11 pm

outer cover layer II (2.1 pm): 99.9% by weight ethylene-propylene copolymer with a melting point of 135 ° C and a melt flow index of 7.3 g / 10 min at 230 ° C and 2.16 kg load (ISO 1133)

0.1% by weight of SiO 2 as an antiblocking agent

The composition and the thickness of all other layers, as well as the conditions during the production of the film remained unchanged.

Example 4

A film was produced as described in Example 3. In contrast to Example 3, the composition of the outer cover layer was changed. The outer cover layer was now built up from the propylene homopolymer of the outer intermediate layer and had a layer thickness of 3.2 μm.

Example 5

A film was produced as described in Example 4. In contrast to Example 4, the outer cover layer, like the inner cover layer, was now made up of incompatible polymers and had the following composition: outer cover layer I (2.3 pm):

- 81.1% by weight of ethylene-propylene copolymer with a melting point of

- 18.8% by weight MDPE with an MFI of 14.4 g / 10 min (21, 6 kg and 190 ° C);

Density of 0.937g / ccm3 and a melting point of 126 ° C 0.1 wt .-% Si02 as an antiblocking agent

Example 6 A film was produced according to Example 4. In contrast to Example 4, the layer thickness of the outer cover layer was increased to 4.7 pm.

Comparative Example 1

A film was produced according to Example 3, in contrast to Example 3, the composition of the outer intermediate layer was changed. The outer intermediate layer now contained no platelet-shaped aluminum particles. The thickness of the layers, as well as the composition of all other layers, as well as the conditions when the film was frozen remained unchanged. The film had a reduced density and a white-opaque look with no metallic appearance.

Comparative Example 2

A film was produced according to Example 5, in contrast to Example 5, the outer intermediate layer did not contain any aluminum particles. Instead, the film was metallized on its outer surface. The thickness of the layers, as well as the composition of all other layers, as well as the conditions when the film was frozen remained unchanged.

It was found that the properties of the film were changed and that the film could no longer be charged. In addition, the film had a slight tendency to curl in the direction of the metal layer after cutting.

Comparative Example 3

The films according to Comparative Example 2 were laminated with the metal side against a transparent BoPP film. This example also showed insufficient charging.

The films according to Examples 1 to 6 could easily be processed into a label and used as an in-mold label in the injection molding process. The labels could be positioned well in the mold and adhered properly in the mold until flinter spraying. As a result, perfectly labeled containers were obtained, which had an attractive label with a high-quality silver-like metallic look. The labeled containers showed a surprisingly similar appearance to the metallized labels. especially the Films according to Examples 4 and 6 were surprisingly distinguished by a particularly high-quality metallic look, which had a shimmering silvery glitter effect after injection molding. The films according to Comparative Examples 2 to 3 showed that although the metallization for in-mold labels provides a perfect metallic appearance, the printability, the charging behavior and thus the positioning, as well as the flatness, were adversely affected.

Fig. 1. Foil structure

table 2: film properties

table 3: application

positioning of the label via electrostatic charging

Claims

1 . In-mold label made of a multilayer, biaxially oriented polypropylene film which comprises at least one vacuole-containing base layer and an outer cover layer and an inner cover layer and an outer intermediate layer, the outer intermediate layer containing platelet-shaped aluminum particles.

2. In-mold label according to claim 1, characterized in that the platelet-shaped aluminum particles have a thickness of <2pm.

3. In-mold label according to one of claims 1 to 2, characterized in that the outer intermediate layer is substantially free of vacuoles.

4. In-mold label according to one of claims 1 to 3, characterized in that the inner cover layer contains a mixture of incompatible polymers, preferably at least one polyethylene and a propylene polymer.

5. In-mold label according to claim 4, characterized in that the polyethylene is an HDPE or an MDPE and the polypropylene polymer is a propylene co- or propylene terpolymer or a propylene homopolymer.

6. In-mold label according to one or more of claims 1 to 5, characterized in that the thickness of the outer intermediate layer is 1 to 6pm.

7. In-mold label according to one or more of claims 1 to 6, characterized in that the outer cover layer is constructed from propylene homopolymer and has a gloss of 40 to 80 at an angle of 20 ° in the gloss measurement.

8. In-mold label according to one or more of claims 1 to 6, characterized in that the outer cover layer is composed of propylene co- and / or propylene terpolymer and has a gloss of 40 to 80 at an angle of 60 ° in the gloss measurement.

9. In-mold label according to one or more of claims 1 to 6, characterized in that the outer cover layer is made of incompatible polymers, preferably polyethylene and propylene polymer, and has a gloss of 5 to <40 at an angle of 60 ° in the gloss measurement.

10. In-mold label according to one or more of claims 1 to 9, characterized in that the film contains no Ti02.

11. In-mold label made from a multi-layer biaxially oriented

Polypropylene film which comprises at least one vacuole-containing base layer and an outer cover layer and an inner cover layer and an outer intermediate layer, the outer cover layer containing platelet-shaped aluminum particles.

12. In-mold label according to claim 11, characterized in that the outer

Intermediate layer contains platelet-shaped aluminum particles.

13. Use of an in-mold label according to one of claims 1 to 12 as an in-mold label in the injection molding process.

14. Decorated container, characterized in that the container comprises an in-mold label according to one of claims 1 to 12.