Patent Application
20180148614
The present invention relates to a multilayer polyolefin film comprising a layer sequence of a sealable layer (a) based on a polyethylene component having a density in the range from 0.910 to 0.940 g/cm3 and a melting point in the range from 110° C. to 130° C., a layer (b) based on a polymer mixture of 51-85 wt % of at least one polyethylene having a density of 0.910 to 0.940 g/cm3 and 15-49 wt %, based in each case on the total weight of the polymer mixture, of at least one propylene homopolymer or copolymer, a sealable layer (c) based on a polyethylene component having a density in the range from 0.910 to 0.940 g/cm3 and a melting point in the range from 110° C. to 130° C., where the melting point of the layer (a) and/or of the layer (c) is at least 5° C. lower than the melting point of the layer (b), and where the tear propagation resistance of the polyolefin film in machine direction [MD] is ≤5 N and the tear propagation resistance crosswise to the machine direction [CD] is at least four times higher than in [MD], measured in each case according to DIN 53356, and the tensile strength is of approximately equal magnitude in machine direction [MD] as crosswise to the machine direction [CD] and is ≥15 N, measured according to DIN ISO 527-3, and to packaging produced therefrom for food, or packaging for preferably individually packaged hygiene products or individually packaged incontinence products, which optionally are self-adhesive.
It is known that polyolefin films can be used for numerous applications, whereby the use of polyolefin films as packaging materials accounting for a considerable proportion of the use. In the case of this use, the packagings, closed usually by sealing, are produced in particular for the food segment and oftentimes cannot be opened trouble-free. Particularly significant is for completely closed packaging, that the packaging can only be opened by tearing one of the sealing seams, so that the packaged contents can easily be spilt. This may even happen with a completely closed packaging which already has an opening aid, i.e., a marker of the direction of tearing for the opening of the packaging, outside a sealing seam region, although the packaging film used as packaging material has a lower tear propagation resistance in the marked opening direction than crosswise to that direction, however, the opening tear is not controlled, but instead has intolerable deviations from a straight, linear tear. Even with this kind of packaging, consequently, uncomplicated handling and removal of the packaged contents—such as, for example, of a packaged food—without scattering or spilling some, or the portioning of, for example, deep-frozen comestibles, is difficult.
For many kinds of packaging, furthermore, a packaging material is also required to have sufficiently high mechanical properties, such as an extremely high puncture resistance and sealing seam strength, in order to facilitate the handling of the packaging produced from the corresponding packaging films. This is especially the case because the filled packages are usually stacked or layered one above another during storage and on transport, and the packagings must not be punctured thereby. This is of course also the case for frozen storage, in order to minimize the proportion of rejected products.
There is therefore a need to provide a packaging film which in addition to sufficiently good mechanical properties is distinguished by an easy, straight and linear tear propagation when a packaging produced from the film is opened.
It was an object of the present invention, therefore, to provide a polyolefin film, suitable as packaging film, which ensures a substantially trouble-free opening of packaging produced from the packaging film, without tearing a sealing seam, and allows trouble-free handling of such packaging.
This object is achieved by the provision of the inventive multilayer polyolefin film, comprising a layer sequence of
The inventive multilayer polyolefin film preferably has a total thickness of 30-120 μm, preferably of 50-100 μm.
The term “layer sequence” in the sense of the invention means that the layers (a), (b) and (c) are present in the order stated and are directly adjacent to one another. Additional layers and/or coatings may optionally be present on a surface of the layer sequence, such as a release coating, for example, preferably composed of cured polysiloxane.
The layer (a) and/or the layer (c) has in each case preferably a layer thickness of 5-30 μm, and the layer (b) a layer thickness of 20-90 μm.
Since the release coating, where present, has a thickness of 1-2 μm at most, it is not referred to as a layer.
The inventive polyolefin film consists preferably, at least to an extent of 95 wt %, of C2-C8 olefin polymers, mixtures thereof or copolymers thereof, and optionally of the auxiliaries recited later on in the description. The polyolefin film of the invention comprises no polybutylene.
The inventive polyolefin film also comprises no cyclic olefin polymers or copolymers.
The inventive polyolefin film has no metal layer such as a metal foil applied, for example, by electrode sputtering or from the vapor phase.
The layer (a) and/or the layer (c) of the inventive polyolefin film is based preferably on a polyethylene component having a density in the range from 0.915 to 0.940 g/cm3 and a melting point in the range from 113° C. to 130° C., and is preferably heat-sealable.
The term “polyethylene component” refers to at least one low-density polyethylene (LDPE), at least one linear low-density polyethylene (LLDPE), or a mixture of LDPE and LLDPE.
The term “polyethylene having a low density” in the sense of the invention is synonymous with the term “low-density polyethylene”, or “LDPE”, i.e., this term refers to unfoamed polyethylene of low density which is notable for a high degree of branching of the molecules, meaning that the polyethylene main chain carries 8 to 40 side chains of repeating ethylene units and has no polymerized units of other olefins. The polyethylenes having a low density used for the layers (a) to (c) preferably have a density in the range from 0.915 to 0.940 g/cm3, more preferably from 0.915 to 0.938 g/cm3.
The polyethylene component of the layer (a) and/or of the layer (c) may also consist of a linear polyethylene having a low density.
The term “linear polyethylene having a low density” in the sense of the invention is synonymous with the term “linear low-density polyethylene” or “LLDPE”, meaning that this term refers to unfoamed, linear, low-density polyethylene which has a low degree of branching of the molecules and preferably has a density in the range from 0.920 to 0.940 g/cm3 and preferably comprises at least one α-olefin having 4-8 carbon atoms, more particularly hexene and/or octene, as comonomer in addition to the ethylene.
The polyethylene component of the layer (a) or of the layer (c) preferably consists of a mixture of 55-80 wt % of LDPE and 45-20 wt % of LLDPE, more preferably of 65-75 wt % of LDPE and 35-25 wt % of LLDPE.
The melting point of the polyethylene component of the layer (a) and/or of the layer (c) is in the range from 110° C. to 130° C. and is lower by at least 5° C. than the melting point of the layer (b).
The term “based on” is understood in accordance with the invention as “is composed of”.
The layer (a) and the layer (c) may be composed identically or differently. The two layers may differ in thickness or composition, however an identical composition for these two layers is preferred. The same applies to the respective layer thickness.
This means that in one preferred embodiment of the inventive multilayer polyolefin film, the layer (a) and the layer (c) have an identical layer construction, preferably an identical layer thickness and/or an identical composition.
The layer (b) is based on a polymer mixture of 51-85 wt % of at least one polyethylene having a density of 0.910 to 0.940 g/cm3 and 15-49 wt %, based in each case on the total weight of the polymer mixture, of at least one propylene homopolymer or copolymer.
The polyethylene present in the polymer mixture for composing the layer (b) is preferably at least one low-density polyethylene (LDPE) or at least one linear low-density polyethylene (LLDPE) or a mixture of LDPE and of LLDPE. Where a mixture of LDPE and LLDPE is used, the mixing ratio is preferably 30:70 wt % to 70:30 wt % of LDPE to LLDPE.
Suitable as second polymer component of the polymer mixture for composing the layer (b) is a propylene homopolymer or propylene (block) copolymer. Preferably, as propylene homopolymer an isotactic propylene homopolymer having a melting point of 140 to 170° C., preferably of 150 to 160° C. is used. Preferably, as propylene copolymer a copolymer of propylene and of up to 20 wt %, preferably ≤15 wt %, of ethylene; with particular preference, a propylene/ethylene block copolymer with at least 3 wt %, more preferably with 4 wt % to 10 wt %, of ethylene may be used.
Preferably, as polymer mixture for the layer (b), a mixture of an LDPE and a propylene/ethylene block copolymer, or a mixture of an LLDPE and a propylene/ethylene block copolymer is used. Preferably, as a polymer mixture for the layer (b) a mixture of LDPE and a propylene homopolymer or a mixture of LLDPE and a propylene homopolymer can also be used.
The inventive multilayer polyolefin film is distinguished by a tear propagation resistance in machine direction (MD) of ≤5 N, preferably ≤3 N, where the tear propagation resistance crosswise to the machine direction (CD) is at least four times higher than in (MD), measured in each case according to DIN 53356, and the tensile strength both in machine direction and crosswise to the machine direction has approximately the same value, preferably in each case ≥15 N, more preferably ≥20 N. Furthermore, the inventive polyolefin film has excellent puncture resistance values.
Each of the layers of the inventive multilayer polyolefin film may contain the same or different additives and/or auxiliaries selected from the group encompassing antioxidants, antiblocking agents, antifogging agents, antistats, active antimicrobial ingredients, light stabilizers, UV absorbers, UV filters, dyes, color pigments, stabilizers, preferably heat stabilizers, process stabilizers, and UV and/or light stabilizers, preferably based on at least one sterically hindered amine (HALS), processing aids, flame retardants, nucleating agents, crystallization agents, preferably crystal nucleus formers, lubricants, optical brighteners, plasticizers, silanes, spacers, fillers, such as CaCO3, silicates, peel additives, sealing additives, waxes, wetting agents, surface-active compounds, preferably surfactants, and dispersing agents.
The layers of the inventive polymeric film may contain at least 0.01-15 wt %, preferably at least 0.1-10 wt %, based in each case on the total weight of an individual layer, of at least one of the before mentioned additives.
For the purpose of achieving a release effect, the inventive polyolefin film may have a release coating (d) on one of its outer layers.
The release coating is preferably based on a cured polysiloxane coating, which is applied to a surface of the inventive packaging film over substantially the whole surface, preferably apart from at least one strip running in machine direction, or over a partial area, preferably as crosswise strips in precise repeat.
The term “polysiloxane” in the sense of the present invention refers to polymers which polymer chains are constructed in alternation of silicon atoms and oxygen atoms. A polysiloxane is based on n repeating siloxane units (—[Si(R2)—O]—)n, which each independently of one another are disubstituted by two organic radicals R, with R preferably in each case being R1 or OR1 and R1 in each case being an alkyl radical or an aryl radical. The cured polysiloxane coating is based preferably on a repeating dialkylsiloxane unit or on a repeating alkylarylsiloxane unit. Depending on how many Si—O bonds an individual siloxane unit has, based in each case on one tetravalent silicon atom, these units may be differentiated into terminal monofunctional siloxanes (M) having one Si—O bond, difunctional siloxanes (D) having two Si—O bonds, trifunctional siloxanes (T) having three Si—O bonds, and tetrafunctional siloxanes (Q) having four Si—O bonds. The inventive polysiloxane coating preferably has a crosslinked cyclic or chain-like structure, more preferably a crosslinked chain-like structure, which is linked by (D), (T) and/or (Q) units to form a two- or three-dimensional network. The number n of the repeating siloxane units (—[Si(R2)—O]—)n in the polysiloxane chain is referred to as the degree of polymerization of the polysiloxane.
The cured polysiloxane coating, where present, of the inventive polyolefin film is based preferably on at least one cured, i.e., crosslinked, polysiloxane selected from the group comprising polysiloxanes which are addition-crosslinked, preferably addition-crosslinked with metal catalysis, condensation-crosslinked, radically crosslinked and/or cationically crosslinked.
With particular preference the polysiloxane coating is based on at least one cured polysiloxane which has been cured by thermal curing and/or with exposure to UV radiation. The polysiloxane coating (d) is based preferably on at least one cured polysiloxane selected from the group encompassing polydialkylsiloxanes, preferably polydimethylsiloxanes, and polyalkylarylsiloxanes, preferably polymethylphenylsiloxanes, each of which are cured. Thermally cured polysiloxanes may be obtained by thermal hydrosilylation of polysiloxanes having silane functions with a compound having at least one carbon double bond. UV curing, like thermal curing, takes place after the production of the inventive polyolefin film, with UV curing being particularly preferred in accordance with the invention.
In principle, the inventive polyolefin film may be produced by known production methods such as by extrusion or by coextrusion, for example.
Either individual layers or all the layers of the inventive multilayer polyolefin film may be produced by extrusion, more particularly by blown film extrusion and/or flat film extrusion (cast extrusion), or coextrusion, preferably blown film coextrusion and/or flat film coextrusion (cast coextrusion), with blown film (co)extrusion being preferred. Care should be taken to ensure that in the event of doping the layer(s) with additives, these additives are employed by blending, optionally as a masterbatch, with the polymer component(s) of the respective layer for processing. This blending may take place dry in pellet/powder form or pellet/pellet form. Alternatively it is possible to add the additive to the molten polymer component(s) of the respective layer, preferably by metered addition in an extruder used for the extrusion of the layer in question.
In the case of production by extrusion, the melts corresponding to the individual layers of the inventive polyolefin film are (co)extruded simultaneously and jointly through an annular die or a flat die, and the resulting film, when using an annular die, is blown up with air, preferably with a blow-up ratio of at least 1:1, more preferably of at least 1.5:1, very preferably of at least 2:1, and cooled, or, when using a flat die, is taken off by means of rollers, for solidification, and cooled.
In another embodiment, the polyolefin film may also be produced as a laminate comprising the coextruded layer sequence (a)-(c).
In a further preferred embodiment, the entire multilayer film is in the form of a preferably coextruded film bubble which may optionally be processed to form a flat-laid film.
With particular preference the inventive polyolefin film is produced as a multilayer blown film, preferably by extrusion, more particularly by blown film coextrusion.
In another embodiment, the inventive polyolefin film may be produced and processed partly or completely as a cast film.
The polyolefin film is preferably unoriented or may be oriented monoaxially in MD.
The polyolefin film produced as cast film may in this case be oriented monoaxially in a draw ratio of at least 1:1.5, preferably at least 1:2, more preferably 1:2 to 1:5.
Subsequently it is possible, optionally, for a release coating to be applied to at least one surface of the inventive polyolefin film, optionally after interim storage of the film.
The inventive polyolefin film may be embossed and may have a single-sided embossing structure on one of its surface layers, or a continuous embossing structure. The embossing methods are known to the skilled person.
A further subject of the invention is therefore the use of the inventive polyolefin film as packaging material.
The inventive polyolefin film is especially suitable for producing packaging, preferably pouch packaging, individual-portion packaging, a sachet or a stick pack.
A further subject of the invention is therefore the use of an inventive polyolefin film for producing packaging, preferably a pouch pack, an individual-portion pack, a sachet or a stick pack.
The inventive polyolefin film is used preferably for producing packaging which is easy to open, since the film has a far lower tear propagation resistance in machine direction than crosswise to the machine direction. As a result, the package contents can easily be withdrawn from such packaging, since when the packaging is torn open and torn further, there is a straight, linear course to the tear. The risk of scattering or spilling of the packaged contents is therefore minimized.
One subject of the present invention is an easy-to-open packaging comprising an inventive polyolefin film.
Features of such an inventive packaging includes, in particular, the feature that it is easy to open, in addition to the easy and straight tear propagation behavior, without any need for a sealing seam of the packaging to be torn open. For the tear-open direction of the inventive packaging, it is also possible, optionally, to make a notch or weakening in the direction of the lower tear propagation resistance of the inventive polyolefin film. If a notch or weakening is made, it ought preferably to be located in the sealing seam region. In one preferred embodiment, the sealing seam strength of the seams of the inventive packaging is greater than the tear propagation resistance in the marked tear-open direction.
A further feature of the inventive packaging is that it has high puncture resistance values, thus giving it very good handling qualities; in other words, during storage, transport, and sale, it is less readily damaged by exposure to impacts than are films having similar tear propagation behavior.
In another preferred embodiment, an inventive polyolefin film is also suitable as release film.
A further subject of the present invention is therefore the use of an inventive polyolefin film as release film, more particularly with a release coatings as surface coating.
Since one of the important factors in such applications is that the release film, optionally with the protected substrate, can be removed easily in the desired length and in a straight, linear course, the inventive polyolefin film is particularly suitable as release film and protective film on account of its particular monoaxial tear-off and/or tear propagation behavior.
A further subject of the present invention, therefore, is the use of the inventive polyolefin film as detachable release film or protective film, preferably for articles of any kind, more preferably for self-adhesive articles of any kind.
Among other applications, therefore, the use of the inventive polyolefin film as detachable packaging film and/or protective film for self-adhesive labels or adhesive tapes of any kind, especially in the building industry, is a further subject of the present invention.
A particularly preferred use of the inventive polyolefin film with a release coating is the use thereof as preferably detachable, flexible packaging film and/or protective film for hygiene articles, preferably individually packaged, optionally folded, possibly self-adhesive panty liners, sanitary towels or incontinence articles. Correspondingly, the inventive polyolefin film takes the form of a preferably detachable packaging wrapper, preferably for the possibly self-adhesive hygiene articles recited, preferably sanitary towels, panty liners or incontinence articles, which are preferably present in individually packaged form in the inventive packaging wrapper.
For each polyolefin film produced from the polymer mixtures specified in table II, determinations were made of the tensile strength in machine direction (MD) and crosswise to the machine direction (CD) in accordance with DIN EN ISO 527-3.
With a sample width of 15 mm, and at a measuring velocity of 500 mm/min, determinations were made of the maximum force in N.
The thickness of the respective polyolefin film was measured in accordance with DIN 53370 and reported as an average value.
The tear propagation resistance of each inventive and comparative polyolefin film was measured according to DIN 53 356, the measurement being carried out on a sample size of 100 mm×50 mm at a measuring velocity of 300 mm/min over a measuring length of 30 mm, with the initial values being disregarded in the evaluation. Determinations were made of the tear propagation resistance in machine direction (MD) and also crosswise to the machine direction (CD).
The values determined both in machine direction (MD) as well as crosswise to the machine direction (CD) not only for the tensile strength but also for the tear propagation resistance have been reported in table III below, in each case for the corresponding polyolefin films.
The puncture resistance of the inventive and of the comparative polyolefin films was determined according to ASTM E 154-88 Part 10 and reported in [N].
The puncture resistance values found are reported below in table IV.
A straight-linear tear propagation behavior on the part of the inventive and comparative polyolefin films is assessed by measuring the deviation from a straight, linear course during tearing (tear propagation or tear removal). This deviation is reported in [mm].
From the polyolefin films whose tear propagation behavior is to be ascertained, 10 samples in each case are cut in such a way that they have a length of 100 mm parallel to the machine direction (MD) and a width of 50 mm crosswise to the machine direction (CD). Furthermore, 10 samples are cut in such a way that they have a length of 100 mm crosswise to the machine direction (CD) and a width of 50 mm parallel to the machine direction (MD).
A 50 mm incision, in the thread direction and parallel to the longitudinal side, is made in the middle of the transverse side of each of the individual samples, and underneath the incision each sample is provided, centrally and parallel to the longitudinal side, with a double-sided adhesive tape having a width of 20 mm and a length of 90 mm. A marker is used to mark a linear extrapolation line from the incision, and this line serves as a straight, linear tearing line for measuring the deviation.
The tear behavior of the individual samples is determined under standard conditions (DIN 50014-23/50-2). For this purpose, one leg of the individual samples is fixed, in each case with the aid of the adhered, double-sided adhesive tape at a defined angle of 45° C. [β] on a metal bar having a width of 100 mm and a length of 350 mm.
The metal bar is clamped into the lower tensioning jaw of an electronic tear destruction instrument (Zwick). The incised end of the unfixed leg (“the unfixed trouser leg”) of the individual samples is fastened by means of a double-sided adhesive tape to a stiff film strip which is approximately 400 mm long, and this strip is clamped into the upper tensioning jaw of the tear destruction instrument.
The two legs of the individual samples are then pulled apart at an angle of 175° and with a velocity of 500 mm/min until the sample is completely separated.
For the assessment of the linear tear propagation behavior of the samples, a determination is made of the maximum deviation A of the tear in mm from the marking line (straight, linear tear extrapolating the incision) at the end of the sample.
From the measured maximum deviations A of the 10 samples with dimensions of 100 mm (MD)×50 mm (CD), the average value is formed. This value serves for assessment of the linear tear behavior in machine direction (MD).
Correspondingly, the average value is likewise formed from the measured maximum deviations A of the 10 samples with dimensions of 100 mm (CD)×50 mm (MD). This average value serves to assess the linear tear behavior crosswise to the machine direction (CD).
The values ascertained are reported below in table IV.
The polyolefin films according to the comparative examples and also to the examples according to table II each consist of three layers and have the specified thickness. The individual layers of each polyolefin film are immediately adjacent to each other in the sequence in which they are listed below. The polyolefin films were each produced by blown film coextrusion. The blow-up ratio in each case was 3:1.
The results set out in tables III and IV for the inventive polyolefin films show that these films have an excellent tensile strength in spite of low tear propagation resistance in CD, and so are suitable as packaging films for the production of packaging having excellent opening characteristics, and also for use as easy-release release films and/or protective films. These results show, furthermore, that the inventive polyolefin films are distinguished by a linear, straight course of the tear on opening, as well as by excellent puncture resistance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 009 546.3 | Jul 2015 | DE | national |
| 10 2015 017 119.4 | Jul 2015 | DE | national |
| 10 2016 006 065.4 | May 2016 | DE | national |
This application is a continuation of International Patent Application No. PCT/EP2016/001295, filed Jul. 27, 2016, which claims foreign priority benefit under 35 U.S.C. § 119 of German Patent Application 10 2015 009 546.3 filed Jul. 28, 2015, German Patent Application 10 2015 017 119.4 filed Jul. 28, 2015, and German Patent Application 10 2016 006 065.4 filed May 19, 2016, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2016/001295 | Jul 2016 | US |
| Child | 15877556 | US |
