HK1191611A - In-mould labelling - Google Patents

Abstract

There is disclosed a method of manufacturing an in-mould labelled article, the method comprising the steps of: placing a label comprising a film having a core comprising polypropylene / polyethylene random copolymer as its principal polymeric constituent into a mould for injection moulding, thermoforming, or blow moulding; holding the label in position; injecting a polymeric melt into, or thermoforming or blowing a polymeric preform in said mould so as to bind with the label; and removing the article from the mould. A process of in-mould labelling using such a label is also disclosed.

Description

In-mold label

The present invention relates to a process for producing an in-mould labelled article using a label comprising a film having a core comprising polypropylene/polyethylene random copolymer as its major polymeric component and one or more additional layers completely covering each surface of the core. A method of in-mold labeling is also disclosed.

In-mold labeling (IML) techniques have been known for many years. It involves the use of paper or plastic labels which ultimately form an integral part of the molded product. Therefore, the in-mold label must be able to withstand the heat applied during the molding process. The resulting product is a pre-decorated article, such as a container or the like, which can then be filled. In contrast to glue applied labels or pressure sensitive labels which appear on the surface of the container, in-mold labels appear as part of the container. Effectively, in-mold labeling eliminates the need for a separate labeling process after container manufacture, which reduces labor and equipment costs.

In-mold labels typically comprise a carrier substrate consisting of a polymeric or cellulosic carrier film with a decorative pattern or written information printed thereon. The label thus obtained is then placed on the wall of a mould for injection moulding or blow moulding or the like, held in place by various means, such as electrostatic forces or vacuum suction, and the polymer article is moulded by injection moulding a mass of polymer melt or by blow moulding a polymer parison against the mould wall to which the in-mould label is applied. This allows the label to be incorporated into the shaped article and can be considered an integral part of the article. The adhesion of such labels to polymeric articles can be enhanced by applying a heat-sealable layer (film or coating) on the back (i.e. the unprinted surface) of the in-mold label to be contacted with the polymeric article.

The in-mold label may be used to cover a portion of the container or to cover the entire outer surface of the container. In the latter case, the in-mold label serves as an additional layer and may therefore enhance the structural integrity of the container.

During the molding of certain articles, such as container lids or parallel sided containers, film shrinkage can cause deformation of the label and/or molded article. For example, such deformation may produce a buckling or bending effect of the article and is highly undesirable. In extreme cases, such deformation may result in a poorly assembled component, such as a lid on a container, or a plurality of containers that are poorly "matable".

Conventionally, the problem of distortion is particularly acute when labels formed from solid biaxially oriented polypropylene films are subjected to in-mould labelling techniques. Thus, cast polypropylene or cavitated biaxially oriented polypropylene films are used as in-mold label substrates.

However, the use of these materials leads to other disadvantages. For example, cast polypropylene is a low stiffness material and therefore labels comprising such material as a substrate must have an increased thickness compared to biaxially oriented polypropylene film in-mold labels to provide acceptable structural properties. In terms of consistency, the conversion and shaping using cast polypropylene is also considered to be inferior to biaxially oriented polypropylene, resulting in reduced throughput and production efficiency.

In addition, the cavitated biaxially oriented polypropylene film switched well, but produced a matte effect label due to collapse of the cavitated structure.

Therefore, efficient and low cost production of gloss effect lids or parallel sided containers using common materials is challenging. It would be of great value to provide an in-mold label that simultaneously exhibits stiffness equivalent to or greater than biaxially oriented polypropylene, deformation equivalent to or less than cast polypropylene or cavitated biaxially oriented polypropylene, and also high clarity.

Therefore, there is a need for a process for in-mold labeling and a film for use in such a process that do not have the above disadvantages. It will be apparent from the following description how the present invention addresses the above-identified deficiencies associated with prior art configurations while presenting numerous additional advantages not heretofore contemplated or attainable by the prior art.

According to the present invention there is provided a process for in-mould labelling of an article with a polymeric film, wherein the film comprises at least one core layer comprising a random copolymer of polypropylene and polyethylene, the film shrinking upon application of heat and exhibiting a maximum shrink force of not more than 500cN in the residual shrinkage immediately after application of heat.

Residual shrinkage can be defined as the continued shrinkage of the film after the heating is stopped. The period of time during which residual shrinkage occurs is typically one or two or three or several minutes following cessation of heating.

Throughout this specification, the maximum shrink force is the maximum shrink force in the longitudinal or transverse direction of the film.

Preferably, the film exhibits a maximum shrink force of no more than 400cN, more preferably no more than 300cN, and most preferably no more than 250cN, in residual shrinkage.

We have found that the shrink force exhibited by the film in shrinking is a critical parameter as long as the efficacy of the film in-mould labelling is taken into account. It is believed that many prior art IML films exhibit excessive shrink forces upon application of heat, which when placed on a container by the IML process, will cause the label film to deform as it cools.

According to the present invention, a method of manufacturing an in-mould labelled article is also contemplated, said method comprising the steps of:

-placing a polymeric film label in a mould for injection moulding, thermoplastic moulding or blow moulding, wherein the film label comprises at least one core layer comprising a random copolymer of polypropylene and polyethylene, the film label shrinking upon application of heat and exhibiting a maximum shrink force of not more than 500cN in the residual shrinkage immediately after application of heat;

-holding the label in place;

-injecting a polymer melt into the mould or thermoforming or blowing a polymer preform in the mould, thereby bonding to the label; and is

-removing the article from the mould.

The core of the film preferably has an inner surface and an outer surface and comprises a polymer component comprising at least about 80 wt% of a polypropylene/polyethylene random copolymer, based on the weight of the polymer component.

Preferably, the film comprises at least one additional layer disposed on each surface of the core such that the surface of the core is not exposed.

Preferably, the thickness of the core is less than 100 μm.

Preferably, the core is substantially free of ethylene propylene rubber (EPDM).

Thus, according to another aspect of the present invention, there is provided a method of in-mould labelling using a label comprising a film having:

-a core having an inner surface and an outer surface and comprising a polymer component comprising at least about 80 wt% of a polypropylene/polyethylene random copolymer, based on the weight of the polymer component, and

-at least one additional layer placed on each surface of the core so that the surface of the core is not exposed,

the core has a thickness of less than 100 μm and is substantially free of ethylene propylene rubber (EPDM).

The layered structure of the film may be produced by coextrusion, lamination, extrusion coating or other or alternative coating, or any combination thereof.

According to another aspect of the invention, the invention also comprises a method of manufacturing an in-mould labelled article, said method comprising the steps of:

-placing a label comprising a film in a mould for injection moulding, thermoplastic moulding or blow moulding, the film having:

-a core having an inner surface and an outer surface and comprising a polymer component comprising at least about 80 wt% of a polypropylene/polyethylene random copolymer, based on the weight of the polymer component, and

-at least one additional layer placed on each surface of the core so that the surface of the core is not exposed,

the core has a thickness of less than 100 μm and is substantially free of ethylene propylene rubber (EPDM);

-holding the label in place;

-injecting a polymer melt into the mould, or thermoforming or blowing a polymer preform in the mould, thereby bonding to the label; and

-removing the article from the mould.

Common to each of these aspects of the invention is a label comprising a film comprising a core comprising a polypropylene/polyethylene random copolymer as its major polymeric component.

The inventors have realized that when biaxially oriented polypropylene films are used as in-mold labels, the deformation effect generally observed is not related to the final degree of shrinkage of the film, but rather is in accordance with the force with which the film shrinks. Although cavitated and cast polypropylene exhibit reduced shrink forces, in-mold labels formed from these materials have low clarity and low stiffness.

It has surprisingly been found that a film having a non-exposed core with a thickness of less than 100 μm comprising a polypropylene/polyethylene random copolymer as its main component and being free of EPDM can be used as or in an in-mold label, which label shows both high clarity and high stiffness and low deformation due to reduced shrinkage forces.

The thickness of the core is preferably less than 100 μm. It has been observed that films comprising an excessively thick core perform less well, especially compared to the usual in-mold label substrates. In preferred embodiments, the maximum thickness of the core is about 90 μm, about 80 μm, about 75 μm, about 70 μm, about 65 μm, about 60 μm, about 55 μm, or about 50 μm.

The core preferably comprises a polymer component comprising at least about 80% by weight of a polypropylene/polyethylene random copolymer. The polymer component of the core may or may not contain other polymers (e.g., homopolymers or copolymers). In preferred embodiments, the polymer component of the core layer comprises at least about 85%, about 90%, about 95%, about 97%, about 98%, or about 99% polypropylene/polyethylene random copolymer by weight of the polymer component. In certain embodiments, the polymer component of the core consists essentially of a polypropylene/polyethylene random copolymer.

In addition to the polymer component, the core may comprise other additives. However, if additives are present, these are preferably present as minor ingredients.

Thus, the core preferably comprises at least about 80% of the polymer component by weight of the core, more preferably at least about 85%, about 90%, or at least about 95% by weight of the core.

The core of the membrane is preferably free of EPDM rubber. This is because the presence of EPDM rubber is likely to result in incompatibility with the random copolymer core material, possibly resulting in voids or adversely affecting optical properties or performance. EPDM can also interfere with the shrink and shrink force properties of the membrane.

The core of the film is preferably disposed between one or more layers. This prevents the core from being exposed when the film is used in an in-mould labelling process and allows the provision of a sealing layer and a printable layer on either side of the core. In some cases, the skin layers on either side of the core may be the same material; or they may be of different materials. In any case, it is preferred to seal the skin layer on the hot melt or blow preform in the mold at a lower temperature than the temperature of the seal core material. At least one skin layer preferably provides a printable surface of higher quality than the core surface.

As mentioned above, the label used in the present invention is advantageous compared to labels known from the prior art, because: they show low shrinkage forces, resulting in reduced deformation during the in-mold labeling process. The film used in the present invention preferably exhibits a maximum shrink force of less than 500cN, preferably less than 400cN, more preferably less than 300cN and most preferably less than 250cN in the residual shrinkage immediately after the film is exposed to a temperature of 120 ℃ for three minutes.

The polymer component of the core layer may optionally comprise a homopolymer and/or copolymer other than a polypropylene/polyethylene random copolymer, including a polyolefin (most preferably polyethylene, polypropylene, polybutylene or blends or copolymers thereof), polystyrene, polyester, polyamide, acetate, biopolymer (e.g., cellulose, polylactic acid, polyhydroxyalkanoate or mixtures or blends thereof), or mixtures or blends thereof.

By way of illustration, the polymer component of the core may consist essentially of:

a) a blend of a PP homopolymer and a PP/PE random copolymer;

b) blends of PP/PE random copolymers and PP/PE diblock copolymers, or

c) PP/PE binary random copolymer

In such an arrangement, the PE content is up to about 50% by weight of the copolymer it is present.

In a preferred embodiment, the core comprises:

(i)80 to 100 wt% of (i) a PP/PE random copolymer; and

(ii)0 to 20 wt% of (ii) a PP/PE diblock copolymer;

(iii) from 0% to 10% of other known suitable additives (e.g. antioxidants, etc.).

Preferred PP/PE random copolymers typically comprise from about 0.1%, about 0.2%, about 0.5%, about 1%, about 2%, about 3%, or about 4% to about 5%, about 6%, about 7%, about 8%, about 9%, or about 10% polyethylene by weight of the copolymer.

Preferred PP/PE diblock copolymers comprise from about 5% to about 50%, more preferably from about 5% to about 12%, and most preferably about 7.5% by weight of polyethylene.

The film may be prepared by any method known in the art including, but not limited to, cast sheet, cast film, and blown film. For example, the film may be prepared by coextrusion, coating or lamination or any combination thereof.

The films made by the present invention can have a variety of thicknesses depending on the application requirements. For example, the film may have a thickness of about 5 μm to about 100 μm, preferably about 10 μm to about 80 μm, and most preferably about 20 μm to about 70 μm.

The film preferably comprises one or more skin layers on the inside and outside of the core. In preferred embodiments, the film independently comprises one, two or three skin layers on the inside and/or outside of the core.

Preferably, the skin layer has a thickness substantially lower than the thickness of the core. For example, the thickness of the skin layer may independently be from about 0.05 μm to about 2 μm, preferably from about 0.075 μm to about 1.5 μm, more preferably from about 0.1 μm to about 1.0 μm, and most preferably from about 0.15 μm to about 0.7 μm.

The skin layers may be independently formed from polyolefins such as polyethylene, polypropylene, polybutylene, or copolymers and/or blends thereof, including copolymers of ethylene and propylene, copolymers of butylene and propylene, or terpolymers of propylene, ethylene, and butylene. Additionally or alternatively, the film may comprise a skin layer formed of or comprising PVDC or polyester.

The use of a PVDC skin is advantageous because it keeps the label oxygen barrier during and after the retort sterilization or cooking process (where high humidity conditions are likely to be encountered in the mould). The PVDC coating inhibits the ingress of oxygen therethrough even under such high humidity conditions. An example of a label comprising a PVDC skin or coating is disclosed in PCT/GB 2011/050153.

The core may be provided as a single core layer. In alternative embodiments, for example where the film is produced by a so-called foaming process, the core may comprise a plurality of core layers joined together by one or more superposed layers. In such an arrangement, the outer surface of the core will be the top surface of the uppermost core layer and the inner surface of the core will be the bottom surface of the lower core layer.

The lamination layer, if present, may be formed of a polyolefin such as polyethylene, polypropylene, polybutylene, or copolymers and/or blends thereof, including copolymers of ethylene and propylene, copolymers of butylene and propylene, or terpolymers of propylene, ethylene, and butylene.

The lamination layer, if present, preferably has a thickness of about 0.1 μm to about 2 μm, more preferably about 0.5 μm to about 1.5 μm.

The membranes used in the present invention may have a symmetrical structure, such as a/B/C/B/a or a/B/a, or may have an asymmetrical structure in which a different number of additional layers are provided on either side of the core, and/or in which the composition of the layers provided on either side of the core is different.

The film is preferably conformable and/or squeezable. The dynamic storage modulus (E') is preferably: (a) from about 600MPa to about 3000MPa measured in the Transverse Direction (TD); and/or (b) from about 1300MPa to about 3000MPa measured in the Machine Direction (MD).

Additionally or alternatively, the dynamic loss modulus (E ") of the film may be: (a) e "in TD is from about 20MPa to about 150 MPa; and/or (b) E' in the MD is from about 70MPa to about 150 MPa.

Suitably, the film of the invention and/or the film used in the invention may exhibit the following values: (i) e "in TD is from about 28MPa to about 136 MPa; (ii) e "in MD is from about 73MPa to about 135 MPa; (iii) e' in TD is from about 630MPa to about 2800 MPa; and/or (iv) E' in MD is from about 1300MPa to about 3000 MPa.

More suitably, the film of the invention and/or the film used in the invention exhibits the following values: (i) e "in TD is from about 56MPa to about 124 MPa; (ii) e "in MD is from about 76MPa to about 122 MPa; (iii) e' in TD is from about 920MPa to about 2430 MPa; and/or (iv) E' in MD is from about 1325MPa to about 2390 MPa.

Most suitably, the film of the invention and/or the film used in the invention exhibits the following values: (i) e "in TD is from about 80MPa to about 111 MPa; (ii) e "in MD is from about 80MPa to about 108 MPa; (iii) e' in TD is from about 1320MPa to about 2060 MPa; and/or (iv) E' in MD is from about 1350MPa to about 2175 MPa.

Specific films that may belong to and/or be used in the present invention show the following values:

e "(TD) ≈ 90 MPa; e "(MD) ≈ 94 MPa; e' (TD) ≈ 1360 MPa; and E' (MD) is approximately equal to 1470 MPa;

e "(TD) about 87 MPa; e "(MD) ≈ 89 MPa; e' (TD) ≈ 1280 MPa; and E' (MD) is approximately equal to 1560 MPa; and/or

E "(TD) 84 MPa; e "(MD) ≈ 90 MPa; e' (TD) ≈ 1340 MPa; and E' (MD) ≈ 1580 MPa.

Details of how the E 'and E' values are calculated are provided in WO 2004/009355.

The film may be made into a balanced film using substantially equal stretch ratios in the machine and transverse directions, or may be non-balanced, wherein the film is substantially more oriented in one direction (MD or TD). Sequential stretching may be used, where heated rolls produce film stretching in the machine direction, followed by a tenter oven for producing stretching in the transverse direction. Alternatively, simultaneous stretching, for example using the so-called foaming method, or stretching using a draw stenter may be performed simultaneously.

The film may be mono-oriented in the machine or transverse direction. However, in a preferred embodiment, the film is biaxially oriented.

The core and/or skin layers of the film may include additives selected from one or more of the following, mixtures thereof, and/or combinations thereof: UV stabilizers, UV absorbers, dyes; pigments, colorants; metallized and/or pseudo-metallized coatings; lubricants, antistatic agents (cationic, anionic and/or nonionic, such as poly (oxyethylene) sorbitan monooleate), antioxidants, surfactants, hardening aids, slip aids (e.g., hot or cold slip aids that improve the ability of the film to slip well on a surface at about room temperature, such as microcrystalline wax); gloss modifiers, prodegradants, barrier coatings to modify the gas and/or moisture permeability properties of the film (e.g. polyvinylidene halides such as PVdC); antiblock aids (e.g., microcrystalline waxes, e.g., having an average particle size of about 0.1 μm to about 0.6 μm); anti-sticking additives (e.g., fumed silica); particulate materials (e.g., talc); additives to reduce the coefficient of friction (COF) (for example terpolymers of about 2-15% by weight of acrylic or methacrylic acid, 10-80% by weight of methyl or ethyl acrylate and 10-80% by weight of methyl methacrylate together with colloidal silica and carnauba wax as described in US 3753769); a sealing additive; additives to improve the adhesion and/or printability of the ink, crosslinkers (e.g. melamine formaldehyde resins); an adhesive layer (e.g., a pressure sensitive adhesive); and/or an adhesive release layer (e.g., used as a liner for release sheet label applications).

The membrane may be constructed of a material to ensure that it is transparent or at least translucent. Alternatively, when an opaque film is desired, the pigment may be provided in a core or additional layer of the film (e.g., 8% to 10%). When a white film is desired, the pigment used may be titanium dioxide.

The film of the present invention may be further treated by corona discharge treatment, for example, to further improve the ink receptivity of the film or film skin.

The label of the present invention may have other layers such as a primer layer, a print layer, an over coat lacquer (over) and the like. These layers may be placed in interfacial contact with the surface of the core or skin (if present).

The films of the present invention may have substantially balanced properties. In preferred films, the values of E 'in the MD and TD are substantially the same, and/or the values of E' in the MD and TD are substantially the same. More preferably, the film has isotropic dynamic modulus (E 'and E') in all directions parallel to the film surface (most preferably, isotropic mechanical properties; e.g., isotropic physical properties). One method to produce a uniformly oriented film is the bubble blown process described herein.

In-mold labeling, the label may be held in place by at least one of vacuum, compressed air, and static electricity.

The label may be placed within the mold by at least one of: the labels are fed into the mould by a conveyor belt, dropped from the magazine into the mould under the action of gravity, and placed by a handling unit, preferably a robot. The use of robots minimizes human error and improves the hygiene of the final product.

The label may cover the entire outer surface of the article. In other embodiments, only a portion of the outer surface of the article may be covered. Label coverage may depend on the intended use of the article.

In a typical in-mold labeling process, the mold itself is chilled so that the molten polymer fed into the mold quickly cools and hardens at the mold surface once injected. Typically, the mold temperature conditions for the melt are 191-232 ℃ and the mold temperature conditions for the mold are 32-66 ℃.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings and in which:

fig. 1 illustrates shrink force measurements at 120 ℃ on white films of the invention and a comparative conventional white IML film.

Fig. 2 illustrates shrink force measurements at 120 ℃ for clear (transparent) films of the invention and comparative conventional clear (transparent) IML films.

Examples

Exemplary types of films are all biaxially oriented five layer laminates constructed by lamination of three layer films including a core layer and skin layers on either side of the core layer. The resulting five-layer structure includes a core layer with an intermediate laminate layer and skin layers on both sides of the core layer. Similar results are expected with an unlaminated monoweb film comprising a core layer and inner and outer skin layers, although thinner films would result therefrom.

1) Measurement of shrinkage force

Film samples were tested using a TST1 heat shrink tester from Lenzing Instruments GmbH & co. A 25mm wide strip of film was cut from each sample in the Machine Direction (MD) and Transverse Direction (TD). Each strip was loaded separately into TST1 and the shrink force was measured under the following conditions: heating at 120 deg.C for 3 min, and cooling at 25 deg.C for 2 min.

The shrink force results are shown in fig. 1 and 2.

Comparing the shrink force results for the standard IML film type (example 3) and the IML film used in the present invention (example 2), it is apparent that the film used in the present invention exhibits significantly lower forces. We have found that this property provides a beneficial effect when the film of the invention is used as an IML label, by generating less force during cooling compared to conventional IML films, thereby reducing distortion.

The same trend in shrink force characteristics can be found when contrasting clear films: conventional IML film example 4 compares the results of example 1 used in the present invention and is shown in fig. 2.

Claims (16)

1. A process for in-mold labeling of an article with a polymeric film, wherein the film comprises at least one core layer comprising a random copolymer of polypropylene and polyethylene, the film shrinking upon application of heat and exhibiting a maximum shrink force of no more than 500cN in the residual shrinkage immediately after application of heat.

2. The method of claim 1, wherein the film exhibits a maximum shrink force of no more than 400cN, optionally no more than 300cN, optionally no more than 250cN, in residual shrinkage.

3. The method of claim 1 or 2, wherein the core of the film has an inner surface and an outer surface and comprises a polymer component comprising at least about 80 wt% of a polypropylene/polyethylene random copolymer, based on the weight of the polymer component.

4. The method of any one of claims 1 to 3, wherein the film comprises at least one additional layer disposed on each surface of the core such that the surface of the core is not exposed.

5. The method of claim 4, wherein the additional layer disposed on the surface of the core is formed of a polyolefin material.

6. The method of claim 5, wherein the additional layer disposed on the surface of the core is independently formed from polyethylene, polypropylene, polybutylene, or copolymers and/or blends thereof.

7. The method of any one of claims 1 to 6, wherein the core has a thickness of less than 100 μm.

8. The method of any one of claims 1-7, wherein the core is substantially free of ethylene propylene rubber (EPDM).

9. The method of any one of claims 1 to 8, comprising the steps of:

-placing a polymeric film label in a mould for injection moulding, thermoplastic moulding or blow moulding, wherein the film label comprises at least one core layer comprising a random copolymer of polypropylene and polyethylene, the film label shrinking upon application of heat and exhibiting a maximum shrink force of not more than 500cN in the residual shrinkage immediately after application of heat;

-holding the label in place;

-injecting a polymer melt into the mould or thermoforming or blowing a polymer preform in the mould, thereby bonding to the label; and

-removing the article from the mould.

10. The method of claim 9 wherein the label is held in place by at least one of vacuum, compressed air, and static electricity.

11. The method of claim 9 or 10, wherein the label is placed within the mold by at least one of: the labels are fed into the mould by a conveyor belt, dropped from a magazine into the mould under the action of gravity, and placed by a handling unit, preferably a robot.

12. The method of any one of claims 9 to 11, wherein the label covers at least about 50% of the entire outer surface of the article.

13. The method of any one of claims 9 to 12, comprising bringing the temperature of the mould to be lower than the temperature of the melt.

14. The method of any one of claims 1 to 13, wherein the core layer consists essentially of a polypropylene/polyethylene random copolymer.

15. The method of any one of claims 1 to 14, wherein the core has a thickness of no more than about 80 μ ι η.

16. A labelled article produced by the process of any one of claims 1 to 15 and substantially free of distortion of its label.